mirror of https://github.com/mkerrisk/man-pages
1219 lines
35 KiB
Groff
1219 lines
35 KiB
Groff
.\" Copyright (C) 2013, Heinrich Schuchardt <xypron.glpk@gmx.de>
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.\" and Copyright (C) 2014, Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" preserved on all copies.
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.\"
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.\" this manual under the conditions for verbatim copying, provided that
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume.
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.\" no responsibility for errors or omissions, or for damages resulting.
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.\" from the use of the information contained herein. The author(s) may.
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.\" not have taken the same level of care in the production of this.
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.\" manual, which is licensed free of charge, as they might when working.
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.TH FANOTIFY 7 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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fanotify \- monitoring filesystem events
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.SH DESCRIPTION
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The fanotify API provides notification and interception of
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filesystem events.
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Use cases include virus scanning and hierarchical storage management.
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In the original fanotify API, only a limited set of events was supported.
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In particular, there was no support for create, delete, and move events.
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The support for those events was added in Linux 5.1.
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(See
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.BR inotify (7)
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for details of an API that did notify those events pre Linux 5.1.)
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.PP
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Additional capabilities compared to the
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.BR inotify (7)
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API include the ability to monitor all of the objects
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in a mounted filesystem,
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the ability to make access permission decisions, and the
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possibility to read or modify files before access by other applications.
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.PP
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The following system calls are used with this API:
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.BR fanotify_init (2),
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.BR fanotify_mark (2),
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.BR read (2),
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.BR write (2),
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and
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.BR close (2).
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.SS fanotify_init(), fanotify_mark(), and notification groups
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The
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.BR fanotify_init (2)
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system call creates and initializes an fanotify notification group
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and returns a file descriptor referring to it.
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.PP
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|
An fanotify notification group is a kernel-internal object that holds
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a list of files, directories, filesystems, and mount points for which
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events shall be created.
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.PP
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For each entry in an fanotify notification group, two bit masks exist: the
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.I mark
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mask and the
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.I ignore
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mask.
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The mark mask defines file activities for which an event shall be created.
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The ignore mask defines activities for which no event shall be generated.
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Having these two types of masks permits a filesystem, mount point, or
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directory to be marked for receiving events, while at the same time
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ignoring events for specific objects under a mount point or directory.
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.PP
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The
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.BR fanotify_mark (2)
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system call adds a file, directory, filesystem, or mount point to a
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notification group and specifies which events
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shall be reported (or ignored), or removes or modifies such an entry.
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.PP
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|
A possible usage of the ignore mask is for a file cache.
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Events of interest for a file cache are modification of a file and closing
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of the same.
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Hence, the cached directory or mount point is to be marked to receive these
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events.
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After receiving the first event informing that a file has been modified,
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the corresponding cache entry will be invalidated.
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No further modification events for this file are of interest until the file
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is closed.
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Hence, the modify event can be added to the ignore mask.
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Upon receiving the close event, the modify event can be removed from the
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ignore mask and the file cache entry can be updated.
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.PP
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The entries in the fanotify notification groups refer to files and
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directories via their inode number and to mounts via their mount ID.
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If files or directories are renamed or moved within the same mount,
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the respective entries survive.
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If files or directories are deleted or moved to another mount or if
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filesystems or mounts are unmounted, the corresponding entries are deleted.
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.SS The event queue
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As events occur on the filesystem objects monitored by a notification group,
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the fanotify system generates events that are collected in a queue.
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These events can then be read (using
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.BR read (2)
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or similar)
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from the fanotify file descriptor
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returned by
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.BR fanotify_init (2).
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.PP
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Two types of events are generated:
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.I notification
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events and
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.I permission
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events.
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Notification events are merely informative and require no action to be taken
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by the receiving application with one exception: if a valid file descriptor
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is provided within a generic event, the file descriptor must be closed.
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Permission events are requests to the receiving application to decide
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whether permission for a file access shall be granted.
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For these events, the recipient must write a response which decides whether
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access is granted or not.
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.PP
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An event is removed from the event queue of the fanotify group
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when it has been read.
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Permission events that have been read are kept in an internal list of the
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fanotify group until either a permission decision has been taken by
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writing to the fanotify file descriptor or the fanotify file descriptor
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is closed.
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.SS Reading fanotify events
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Calling
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.BR read (2)
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for the file descriptor returned by
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.BR fanotify_init (2)
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blocks (if the flag
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.B FAN_NONBLOCK
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is not specified in the call to
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.BR fanotify_init (2))
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until either a file event occurs or the call is interrupted by a signal
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(see
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.BR signal (7)).
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.PP
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The use of one of the flags
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.BR FAN_REPORT_FID ,
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.BR FAN_REPORT_DIR_FID
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in
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.BR fanotify_init (2)
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influences what data structures are returned to the event listener for each
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event.
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Events reported to a group initialized with one of these flags will
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use file handles to identify filesystem objects instead of file descriptors.
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.TP
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After a successful
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.BR read (2),
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the read buffer contains one or more of the following structures:
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.PP
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.in +4n
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.EX
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struct fanotify_event_metadata {
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__u32 event_len;
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__u8 vers;
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__u8 reserved;
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__u16 metadata_len;
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__aligned_u64 mask;
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__s32 fd;
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__s32 pid;
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};
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.EE
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.in
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.PP
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In case of an fanotify group that identifies filesystem objects by file
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handles, you should also expect to receive one or more additional information
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records of the structure detailed below following the generic
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.I fanotify_event_metadata
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structure within the read buffer:
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.PP
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.in +4n
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.EX
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struct fanotify_event_info_header {
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__u8 info_type;
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__u8 pad;
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__u16 len;
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};
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struct fanotify_event_info_fid {
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struct fanotify_event_info_header hdr;
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__kernel_fsid_t fsid;
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unsigned char file_handle[0];
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};
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.EE
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.in
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.PP
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For performance reasons, it is recommended to use a large
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buffer size (for example, 4096 bytes),
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so that multiple events can be retrieved by a single
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.BR read (2).
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.PP
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The return value of
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.BR read (2)
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is the number of bytes placed in the buffer,
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or \-1 in case of an error (but see BUGS).
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.PP
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The fields of the
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.I fanotify_event_metadata
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structure are as follows:
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.TP
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.I event_len
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This is the length of the data for the current event and the offset
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to the next event in the buffer.
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Unless the group identifies filesystem objects by file handles, the value of
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.I event_len
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is always
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.BR FAN_EVENT_METADATA_LEN .
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For a group that identifies filesystem objects by file handles,
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.I event_len
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also includes the variable length file identifier records.
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.TP
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.I vers
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This field holds a version number for the structure.
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It must be compared to
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.B FANOTIFY_METADATA_VERSION
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to verify that the structures returned at run time match
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the structures defined at compile time.
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|
In case of a mismatch, the application should abandon trying to use the
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fanotify file descriptor.
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.TP
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.I reserved
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This field is not used.
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.TP
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.I metadata_len
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This is the length of the structure.
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The field was introduced to facilitate the implementation of
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optional headers per event type.
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No such optional headers exist in the current implementation.
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.TP
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.I mask
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This is a bit mask describing the event (see below).
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.TP
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.I fd
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This is an open file descriptor for the object being accessed, or
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.B FAN_NOFD
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|
if a queue overflow occurred.
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With an fanotify group that identifies filesystem objects by file handles,
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applications should expect this value to be set to
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.B FAN_NOFD
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for each event that is received.
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The file descriptor can be used to access the contents
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of the monitored file or directory.
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The reading application is responsible for closing this file descriptor.
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.IP
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When calling
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.BR fanotify_init (2),
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|
the caller may specify (via the
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.I event_f_flags
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argument) various file status flags that are to be set
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on the open file description that corresponds to this file descriptor.
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|
In addition, the (kernel-internal)
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.B FMODE_NONOTIFY
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file status flag is set on the open file description.
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|
This flag suppresses fanotify event generation.
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|
Hence, when the receiver of the fanotify event accesses the notified file or
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directory using this file descriptor, no additional events will be created.
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.TP
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.I pid
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If flag
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.B FAN_REPORT_TID
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was set in
|
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.BR fanotify_init (2),
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|
this is the TID of the thread that caused the event.
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Otherwise, this the PID of the process that caused the event.
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.PP
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|
A program listening to fanotify events can compare this PID
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|
to the PID returned by
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.BR getpid (2),
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|
to determine whether the event is caused by the listener itself,
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|
or is due to a file access by another process.
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.PP
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|
The bit mask in
|
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.I mask
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indicates which events have occurred for a single filesystem object.
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Multiple bits may be set in this mask,
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if more than one event occurred for the monitored filesystem object.
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|
In particular,
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|
consecutive events for the same filesystem object and originating from the
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same process may be merged into a single event, with the exception that two
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permission events are never merged into one queue entry.
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.PP
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|
The bits that may appear in
|
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.I mask
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are as follows:
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.TP
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.B FAN_ACCESS
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A file or a directory (but see BUGS) was accessed (read).
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.TP
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.B FAN_OPEN
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A file or a directory was opened.
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.TP
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.B FAN_OPEN_EXEC
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A file was opened with the intent to be executed.
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See NOTES in
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.BR fanotify_mark (2)
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for additional details.
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.TP
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.B FAN_ATTRIB
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A file or directory metadata was changed.
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.TP
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.B FAN_CREATE
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A child file or directory was created in a watched parent.
|
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.TP
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.B FAN_DELETE
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|
A child file or directory was deleted in a watched parent.
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.TP
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.B FAN_DELETE_SELF
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|
A watched file or directory was deleted.
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.TP
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|
.B FAN_MOVED_FROM
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|
A file or directory has been moved from a watched parent directory.
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.TP
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.B FAN_MOVED_TO
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|
A file or directory has been moved to a watched parent directory.
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.TP
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.B FAN_MOVE_SELF
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|
A watched file or directory was moved.
|
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.TP
|
|
.B FAN_MODIFY
|
|
A file was modified.
|
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.TP
|
|
.B FAN_CLOSE_WRITE
|
|
A file that was opened for writing
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.RB ( O_WRONLY
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or
|
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.BR O_RDWR )
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|
was closed.
|
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.TP
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.B FAN_CLOSE_NOWRITE
|
|
A file or directory that was opened read-only
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.RB ( O_RDONLY )
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was closed.
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.TP
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.B FAN_Q_OVERFLOW
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The event queue exceeded the limit of 16384 entries.
|
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This limit can be overridden by specifying the
|
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.BR FAN_UNLIMITED_QUEUE
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flag when calling
|
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.BR fanotify_init (2).
|
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.TP
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.B FAN_ACCESS_PERM
|
|
An application wants to read a file or directory, for example using
|
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.BR read (2)
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|
or
|
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.BR readdir (2).
|
|
The reader must write a response (as described below)
|
|
that determines whether the permission to
|
|
access the filesystem object shall be granted.
|
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.TP
|
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.B FAN_OPEN_PERM
|
|
An application wants to open a file or directory.
|
|
The reader must write a response that determines whether the permission to
|
|
open the filesystem object shall be granted.
|
|
.TP
|
|
.B FAN_OPEN_EXEC_PERM
|
|
An application wants to open a file for execution.
|
|
The reader must write a response that determines whether the permission to
|
|
open the filesystem object for execution shall be granted.
|
|
See NOTES in
|
|
.BR fanotify_mark (2)
|
|
for additional details.
|
|
.PP
|
|
To check for any close event, the following bit mask may be used:
|
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.TP
|
|
.B FAN_CLOSE
|
|
A file was closed.
|
|
This is a synonym for:
|
|
.IP
|
|
FAN_CLOSE_WRITE | FAN_CLOSE_NOWRITE
|
|
.PP
|
|
To check for any move event, the following bit mask may be used:
|
|
.TP
|
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.B FAN_MOVE
|
|
A file or directory was moved.
|
|
This is a synonym for:
|
|
.IP
|
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FAN_MOVED_FROM | FAN_MOVED_TO
|
|
.PP
|
|
The following bits may appear in
|
|
.I mask
|
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only in conjunction with other event type bits:
|
|
.TP
|
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.B FAN_ONDIR
|
|
The events described in the
|
|
.I mask
|
|
have occurred on a directory object.
|
|
Reporting events on directories requires setting this flag in the mark mask.
|
|
See
|
|
.BR fanotify_mark (2)
|
|
for additional details.
|
|
The
|
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.BR FAN_ONDIR
|
|
flag is reported in an event mask only if the fanotify group identifies
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filesystem objects by file handles.
|
|
.PP
|
|
The fields of the
|
|
.I fanotify_event_info_fid
|
|
structure are as follows:
|
|
.TP
|
|
.I hdr
|
|
This is a structure of type
|
|
.IR fanotify_event_info_header .
|
|
It is a generic header that contains information used to describe an
|
|
additional information record attached to the event.
|
|
For example, when an fanotify file descriptor is created using
|
|
.BR FAN_REPORT_FID ,
|
|
a single information record is expected to be attached to the event with
|
|
.I info_type
|
|
field value of
|
|
.BR FAN_EVENT_INFO_TYPE_FID .
|
|
When an fanotify file descriptor is created using the combination of
|
|
.BR FAN_REPORT_FID
|
|
and
|
|
.BR FAN_REPORT_DIR_FID ,
|
|
there may be two information records attached to the event:
|
|
one with
|
|
.I info_type
|
|
field value of
|
|
.BR FAN_EVENT_INFO_TYPE_DFID ,
|
|
identifying a parent directory object, and one with
|
|
.I info_type
|
|
field value of
|
|
.BR FAN_EVENT_INFO_TYPE_FID ,
|
|
identifying a non-directory object.
|
|
The
|
|
.I fanotify_event_info_header
|
|
contains a
|
|
.I len
|
|
field.
|
|
The value of
|
|
.I len
|
|
is the size of the additional information record including the
|
|
.IR fanotify_event_info_header
|
|
itself.
|
|
The total size of all additional information records is not expected
|
|
to be bigger than
|
|
(
|
|
.IR event_len
|
|
\-
|
|
.IR metadata_len
|
|
).
|
|
.TP
|
|
.I fsid
|
|
This is a unique identifier of the filesystem containing the object
|
|
associated with the event.
|
|
It is a structure of type
|
|
.I __kernel_fsid_t
|
|
and contains the same value as
|
|
.I f_fsid
|
|
when calling
|
|
.BR statfs (2).
|
|
.TP
|
|
.I file_handle
|
|
This is a variable length structure of type struct file_handle.
|
|
It is an opaque handle that corresponds to a specified object on a
|
|
filesystem as returned by
|
|
.BR name_to_handle_at (2).
|
|
It can be used to uniquely identify a file on a filesystem and can be
|
|
passed as an argument to
|
|
.BR open_by_handle_at (2).
|
|
Note that for the directory entry modification events
|
|
.BR FAN_CREATE ,
|
|
.BR FAN_DELETE ,
|
|
and
|
|
.BR FAN_MOVE ,
|
|
the
|
|
.IR file_handle
|
|
identifies the modified directory and not the created/deleted/moved child
|
|
object.
|
|
If the value of
|
|
.I info_type
|
|
field is
|
|
.BR FAN_EVENT_INFO_TYPE_DFID_NAME ,
|
|
the file handle is followed by a null terminated string that identifies the
|
|
created/deleted/moved directory entry name.
|
|
For other events such as
|
|
.BR FAN_OPEN ,
|
|
.BR FAN_ATTRIB ,
|
|
.BR FAN_DELETE_SELF ,
|
|
and
|
|
.BR FAN_MOVE_SELF ,
|
|
if the value of
|
|
.I info_type
|
|
field is
|
|
.BR FAN_EVENT_INFO_TYPE_FID ,
|
|
the
|
|
.IR file_handle
|
|
identifies the object correlated to the event.
|
|
If the value of
|
|
.I info_type
|
|
field is
|
|
.BR FAN_EVENT_INFO_TYPE_DFID ,
|
|
the
|
|
.IR file_handle
|
|
identifies the directory object correlated to the event or the parent directory
|
|
of a non-directory object correlated to the event.
|
|
If the value of
|
|
.I info_type
|
|
field is
|
|
.BR FAN_EVENT_INFO_TYPE_DFID_NAME ,
|
|
the
|
|
.IR file_handle
|
|
identifies the same directory object that would be reported with
|
|
.BR FAN_EVENT_INFO_TYPE_DFID
|
|
and the file handle is followed by a null terminated string that identifies the
|
|
name of a directory entry in that directory, or '.' to identify the directory
|
|
object itself.
|
|
.PP
|
|
The following macros are provided to iterate over a buffer containing
|
|
fanotify event metadata returned by a
|
|
.BR read (2)
|
|
from an fanotify file descriptor:
|
|
.TP
|
|
.B FAN_EVENT_OK(meta, len)
|
|
This macro checks the remaining length
|
|
.I len
|
|
of the buffer
|
|
.I meta
|
|
against the length of the metadata structure and the
|
|
.I event_len
|
|
field of the first metadata structure in the buffer.
|
|
.TP
|
|
.B FAN_EVENT_NEXT(meta, len)
|
|
This macro uses the length indicated in the
|
|
.I event_len
|
|
field of the metadata structure pointed to by
|
|
.IR meta
|
|
to calculate the address of the next metadata structure that follows
|
|
.IR meta .
|
|
.I len
|
|
is the number of bytes of metadata that currently remain in the buffer.
|
|
The macro returns a pointer to the next metadata structure that follows
|
|
.IR meta ,
|
|
and reduces
|
|
.I len
|
|
by the number of bytes in the metadata structure that
|
|
has been skipped over (i.e., it subtracts
|
|
.IR meta\->event_len
|
|
from
|
|
.IR len ).
|
|
.PP
|
|
In addition, there is:
|
|
.TP
|
|
.B FAN_EVENT_METADATA_LEN
|
|
This macro returns the size (in bytes) of the structure
|
|
.IR fanotify_event_metadata .
|
|
This is the minimum size (and currently the only size) of any event metadata.
|
|
.\"
|
|
.SS Monitoring an fanotify file descriptor for events
|
|
When an fanotify event occurs, the fanotify file descriptor indicates as
|
|
readable when passed to
|
|
.BR epoll (7),
|
|
.BR poll (2),
|
|
or
|
|
.BR select (2).
|
|
.SS Dealing with permission events
|
|
For permission events, the application must
|
|
.BR write (2)
|
|
a structure of the following form to the
|
|
fanotify file descriptor:
|
|
.PP
|
|
.in +4n
|
|
.EX
|
|
struct fanotify_response {
|
|
__s32 fd;
|
|
__u32 response;
|
|
};
|
|
.EE
|
|
.in
|
|
.PP
|
|
The fields of this structure are as follows:
|
|
.TP
|
|
.I fd
|
|
This is the file descriptor from the structure
|
|
.IR fanotify_event_metadata .
|
|
.TP
|
|
.I response
|
|
This field indicates whether or not the permission is to be granted.
|
|
Its value must be either
|
|
.B FAN_ALLOW
|
|
to allow the file operation or
|
|
.B FAN_DENY
|
|
to deny the file operation.
|
|
.PP
|
|
If access is denied, the requesting application call will receive an
|
|
.BR EPERM
|
|
error.
|
|
Additionally, if the notification group has been created with the
|
|
.B FAN_ENABLE_AUDIT
|
|
flag, then the
|
|
.B FAN_AUDIT
|
|
flag can be set in the
|
|
.I response
|
|
field.
|
|
In that case, the audit subsystem will log information about the access
|
|
decision to the audit logs.
|
|
.\"
|
|
.SS Closing the fanotify file descriptor
|
|
When all file descriptors referring to the fanotify notification group are
|
|
closed, the fanotify group is released and its resources
|
|
are freed for reuse by the kernel.
|
|
Upon
|
|
.BR close (2),
|
|
outstanding permission events will be set to allowed.
|
|
.SS /proc/[pid]/fdinfo
|
|
The file
|
|
.I /proc/[pid]/fdinfo/[fd]
|
|
contains information about fanotify marks for file descriptor
|
|
.I fd
|
|
of process
|
|
.IR pid .
|
|
See
|
|
.BR proc (5)
|
|
for details.
|
|
.SH ERRORS
|
|
In addition to the usual errors for
|
|
.BR read (2),
|
|
the following errors can occur when reading from the
|
|
fanotify file descriptor:
|
|
.TP
|
|
.B EINVAL
|
|
The buffer is too small to hold the event.
|
|
.TP
|
|
.B EMFILE
|
|
The per-process limit on the number of open files has been reached.
|
|
See the description of
|
|
.B RLIMIT_NOFILE
|
|
in
|
|
.BR getrlimit (2).
|
|
.TP
|
|
.B ENFILE
|
|
The system-wide limit on the total number of open files has been reached.
|
|
See
|
|
.I /proc/sys/fs/file\-max
|
|
in
|
|
.BR proc (5).
|
|
.TP
|
|
.B ETXTBSY
|
|
This error is returned by
|
|
.BR read (2)
|
|
if
|
|
.B O_RDWR
|
|
or
|
|
.B O_WRONLY
|
|
was specified in the
|
|
.I event_f_flags
|
|
argument when calling
|
|
.BR fanotify_init (2)
|
|
and an event occurred for a monitored file that is currently being executed.
|
|
.PP
|
|
In addition to the usual errors for
|
|
.BR write (2),
|
|
the following errors can occur when writing to the fanotify file descriptor:
|
|
.TP
|
|
.B EINVAL
|
|
Fanotify access permissions are not enabled in the kernel configuration
|
|
or the value of
|
|
.I response
|
|
in the response structure is not valid.
|
|
.TP
|
|
.B ENOENT
|
|
The file descriptor
|
|
.I fd
|
|
in the response structure is not valid.
|
|
This may occur when a response for the permission event has already been
|
|
written.
|
|
.SH VERSIONS
|
|
The fanotify API was introduced in version 2.6.36 of the Linux kernel and
|
|
enabled in version 2.6.37.
|
|
Fdinfo support was added in version 3.8.
|
|
.SH CONFORMING TO
|
|
The fanotify API is Linux-specific.
|
|
.SH NOTES
|
|
The fanotify API is available only if the kernel was built with the
|
|
.B CONFIG_FANOTIFY
|
|
configuration option enabled.
|
|
In addition, fanotify permission handling is available only if the
|
|
.B CONFIG_FANOTIFY_ACCESS_PERMISSIONS
|
|
configuration option is enabled.
|
|
.SS Limitations and caveats
|
|
Fanotify reports only events that a user-space program triggers through the
|
|
filesystem API.
|
|
As a result,
|
|
it does not catch remote events that occur on network filesystems.
|
|
.PP
|
|
The fanotify API does not report file accesses and modifications that
|
|
may occur because of
|
|
.BR mmap (2),
|
|
.BR msync (2),
|
|
and
|
|
.BR munmap (2).
|
|
.PP
|
|
Events for directories are created only if the directory itself is opened,
|
|
read, and closed.
|
|
Adding, removing, or changing children of a marked directory does not create
|
|
events for the monitored directory itself.
|
|
.PP
|
|
Fanotify monitoring of directories is not recursive:
|
|
to monitor subdirectories under a directory,
|
|
additional marks must be created.
|
|
The
|
|
.B FAN_CREATE
|
|
event can be used for detecting when a subdirectory has been created under
|
|
a marked directory.
|
|
An additional mark must then be set on the newly created subdirectory.
|
|
This approach is racy, because it can lose events that occurred inside the
|
|
newly created subdirectory, before a mark is added on that subdirectory.
|
|
Monitoring mounts offers the capability to monitor a whole directory tree
|
|
in a race-free manner.
|
|
Monitoring filesystems offers the capability to monitor changes made from
|
|
any mount of a filesystem instance in a race-free manner.
|
|
.PP
|
|
The event queue can overflow.
|
|
In this case, events are lost.
|
|
.SH BUGS
|
|
Before Linux 3.19,
|
|
.BR fallocate (2)
|
|
did not generate fanotify events.
|
|
Since Linux 3.19,
|
|
.\" commit 820c12d5d6c0890bc93dd63893924a13041fdc35
|
|
calls to
|
|
.BR fallocate (2)
|
|
generate
|
|
.B FAN_MODIFY
|
|
events.
|
|
.PP
|
|
As of Linux 3.17,
|
|
the following bugs exist:
|
|
.IP * 3
|
|
On Linux, a filesystem object may be accessible through multiple paths,
|
|
for example, a part of a filesystem may be remounted using the
|
|
.IR \-\-bind
|
|
option of
|
|
.BR mount (8).
|
|
A listener that marked a mount will be notified only of events that were
|
|
triggered for a filesystem object using the same mount.
|
|
Any other event will pass unnoticed.
|
|
.IP *
|
|
.\" FIXME . A patch was proposed.
|
|
When an event is generated,
|
|
no check is made to see whether the user ID of the
|
|
receiving process has authorization to read or write the file
|
|
before passing a file descriptor for that file.
|
|
This poses a security risk, when the
|
|
.B CAP_SYS_ADMIN
|
|
capability is set for programs executed by unprivileged users.
|
|
.IP *
|
|
If a call to
|
|
.BR read (2)
|
|
processes multiple events from the fanotify queue and an error occurs,
|
|
the return value will be the total length of the events successfully
|
|
copied to the user-space buffer before the error occurred.
|
|
The return value will not be \-1, and
|
|
.I errno
|
|
will not be set.
|
|
Thus, the reading application has no way to detect the error.
|
|
.SH EXAMPLES
|
|
The two example programs below demonstrate the usage of the fanotify API.
|
|
.SS Example program: fanotify_example.c
|
|
The first program is an example of fanotify being
|
|
used with its event object information passed in the form of a file
|
|
descriptor.
|
|
The program marks the mount point passed as a command-line argument and
|
|
waits for events of type
|
|
.B FAN_OPEN_PERM
|
|
and
|
|
.BR FAN_CLOSE_WRITE .
|
|
When a permission event occurs, a
|
|
.B FAN_ALLOW
|
|
response is given.
|
|
.PP
|
|
The following shell session shows an example of
|
|
running this program.
|
|
This session involved editing the file
|
|
.IR /home/user/temp/notes .
|
|
Before the file was opened, a
|
|
.B FAN_OPEN_PERM
|
|
event occurred.
|
|
After the file was closed, a
|
|
.B FAN_CLOSE_WRITE
|
|
event occurred.
|
|
Execution of the program ends when the user presses the ENTER key.
|
|
.PP
|
|
.in +4n
|
|
.EX
|
|
# \fB./fanotify_example /home\fP
|
|
Press enter key to terminate.
|
|
Listening for events.
|
|
FAN_OPEN_PERM: File /home/user/temp/notes
|
|
FAN_CLOSE_WRITE: File /home/user/temp/notes
|
|
|
|
Listening for events stopped.
|
|
.EE
|
|
.in
|
|
.SS Program source: fanotify_example.c
|
|
\&
|
|
.EX
|
|
#define _GNU_SOURCE /* Needed to get O_LARGEFILE definition */
|
|
#include <errno.h>
|
|
#include <fcntl.h>
|
|
#include <limits.h>
|
|
#include <poll.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sys/fanotify.h>
|
|
#include <unistd.h>
|
|
|
|
/* Read all available fanotify events from the file descriptor \(aqfd\(aq. */
|
|
|
|
static void
|
|
handle_events(int fd)
|
|
{
|
|
const struct fanotify_event_metadata *metadata;
|
|
struct fanotify_event_metadata buf[200];
|
|
ssize_t len;
|
|
char path[PATH_MAX];
|
|
ssize_t path_len;
|
|
char procfd_path[PATH_MAX];
|
|
struct fanotify_response response;
|
|
|
|
/* Loop while events can be read from fanotify file descriptor. */
|
|
|
|
for (;;) {
|
|
|
|
/* Read some events. */
|
|
|
|
len = read(fd, buf, sizeof(buf));
|
|
if (len == \-1 && errno != EAGAIN) {
|
|
perror("read");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* Check if end of available data reached. */
|
|
|
|
if (len <= 0)
|
|
break;
|
|
|
|
/* Point to the first event in the buffer. */
|
|
|
|
metadata = buf;
|
|
|
|
/* Loop over all events in the buffer. */
|
|
|
|
while (FAN_EVENT_OK(metadata, len)) {
|
|
|
|
/* Check that run\-time and compile\-time structures match. */
|
|
|
|
if (metadata\->vers != FANOTIFY_METADATA_VERSION) {
|
|
fprintf(stderr,
|
|
"Mismatch of fanotify metadata version.\en");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* metadata\->fd contains either FAN_NOFD, indicating a
|
|
queue overflow, or a file descriptor (a nonnegative
|
|
integer). Here, we simply ignore queue overflow. */
|
|
|
|
if (metadata\->fd >= 0) {
|
|
|
|
/* Handle open permission event. */
|
|
|
|
if (metadata\->mask & FAN_OPEN_PERM) {
|
|
printf("FAN_OPEN_PERM: ");
|
|
|
|
/* Allow file to be opened. */
|
|
|
|
response.fd = metadata\->fd;
|
|
response.response = FAN_ALLOW;
|
|
write(fd, &response, sizeof(response));
|
|
}
|
|
|
|
/* Handle closing of writable file event. */
|
|
|
|
if (metadata\->mask & FAN_CLOSE_WRITE)
|
|
printf("FAN_CLOSE_WRITE: ");
|
|
|
|
/* Retrieve and print pathname of the accessed file. */
|
|
|
|
snprintf(procfd_path, sizeof(procfd_path),
|
|
"/proc/self/fd/%d", metadata\->fd);
|
|
path_len = readlink(procfd_path, path,
|
|
sizeof(path) \- 1);
|
|
if (path_len == \-1) {
|
|
perror("readlink");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
path[path_len] = \(aq\e0\(aq;
|
|
printf("File %s\en", path);
|
|
|
|
/* Close the file descriptor of the event. */
|
|
|
|
close(metadata\->fd);
|
|
}
|
|
|
|
/* Advance to next event. */
|
|
|
|
metadata = FAN_EVENT_NEXT(metadata, len);
|
|
}
|
|
}
|
|
}
|
|
|
|
int
|
|
main(int argc, char *argv[])
|
|
{
|
|
char buf;
|
|
int fd, poll_num;
|
|
nfds_t nfds;
|
|
struct pollfd fds[2];
|
|
|
|
/* Check mount point is supplied. */
|
|
|
|
if (argc != 2) {
|
|
fprintf(stderr, "Usage: %s MOUNT\en", argv[0]);
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
printf("Press enter key to terminate.\en");
|
|
|
|
/* Create the file descriptor for accessing the fanotify API. */
|
|
|
|
fd = fanotify_init(FAN_CLOEXEC | FAN_CLASS_CONTENT | FAN_NONBLOCK,
|
|
O_RDONLY | O_LARGEFILE);
|
|
if (fd == \-1) {
|
|
perror("fanotify_init");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* Mark the mount for:
|
|
\- permission events before opening files
|
|
\- notification events after closing a write\-enabled
|
|
file descriptor. */
|
|
|
|
if (fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_MOUNT,
|
|
FAN_OPEN_PERM | FAN_CLOSE_WRITE, AT_FDCWD,
|
|
argv[1]) == \-1) {
|
|
perror("fanotify_mark");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* Prepare for polling. */
|
|
|
|
nfds = 2;
|
|
|
|
fds[0].fd = STDIN_FILENO; /* Console input */
|
|
fds[0].events = POLLIN;
|
|
|
|
fds[1].fd = fd; /* Fanotify input */
|
|
fds[1].events = POLLIN;
|
|
|
|
/* This is the loop to wait for incoming events. */
|
|
|
|
printf("Listening for events.\en");
|
|
|
|
while (1) {
|
|
poll_num = poll(fds, nfds, \-1);
|
|
if (poll_num == \-1) {
|
|
if (errno == EINTR) /* Interrupted by a signal */
|
|
continue; /* Restart poll() */
|
|
|
|
perror("poll"); /* Unexpected error */
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
if (poll_num > 0) {
|
|
if (fds[0].revents & POLLIN) {
|
|
|
|
/* Console input is available: empty stdin and quit. */
|
|
|
|
while (read(STDIN_FILENO, &buf, 1) > 0 && buf != \(aq\en\(aq)
|
|
continue;
|
|
break;
|
|
}
|
|
|
|
if (fds[1].revents & POLLIN) {
|
|
|
|
/* Fanotify events are available. */
|
|
|
|
handle_events(fd);
|
|
}
|
|
}
|
|
}
|
|
|
|
printf("Listening for events stopped.\en");
|
|
exit(EXIT_SUCCESS);
|
|
}
|
|
.EE
|
|
.\"
|
|
.SS Example program: fanotify_fid.c
|
|
The second program is an example of fanotify being used with a group that
|
|
identifies objects by file handles.
|
|
The program marks the filesystem object that is passed as
|
|
a command-line argument
|
|
and waits until an event of type
|
|
.B FAN_CREATE
|
|
has occurred.
|
|
The event mask indicates which type of filesystem object\(emeither
|
|
a file or a directory\(emwas created.
|
|
Once all events have been read from the buffer and processed accordingly,
|
|
the program simply terminates.
|
|
.PP
|
|
The following shell sessions show two different invocations of
|
|
this program, with different actions performed on a watched object.
|
|
.PP
|
|
The first session shows a mark being placed on
|
|
.IR /home/user .
|
|
This is followed by the creation of a regular file,
|
|
.IR /home/user/testfile.txt .
|
|
This results in a
|
|
.B FAN_CREATE
|
|
event being generated and reported against the file's parent watched
|
|
directory object and with the created file name.
|
|
Program execution ends once all events captured within the buffer have
|
|
been processed.
|
|
.PP
|
|
.in +4n
|
|
.EX
|
|
# \fB./fanotify_fid /home/user\fP
|
|
Listening for events.
|
|
FAN_CREATE (file created):
|
|
Directory /home/user has been modified.
|
|
Entry \(aqtestfile.txt\(aq is not a subdirectory.
|
|
All events processed successfully. Program exiting.
|
|
|
|
$ \fBtouch /home/user/testfile.txt\fP # In another terminal
|
|
.EE
|
|
.in
|
|
.PP
|
|
The second session shows a mark being placed on
|
|
.IR /home/user .
|
|
This is followed by the creation of a directory,
|
|
.IR /home/user/testdir .
|
|
This specific action results in a
|
|
.B FAN_CREATE
|
|
event being generated and is reported with the
|
|
.B FAN_ONDIR
|
|
flag set and with the created directory name.
|
|
.PP
|
|
.in +4n
|
|
.EX
|
|
# \fB./fanotify_fid /home/user\fP
|
|
Listening for events.
|
|
FAN_CREATE | FAN_ONDIR (subdirectory created):
|
|
Directory /home/user has been modified.
|
|
Entry \(aqtestdir\(aq is a subdirectory.
|
|
All events processed successfully. Program exiting.
|
|
|
|
$ \fBmkdir \-p /home/user/testdir\fP # In another terminal
|
|
.EE
|
|
.in
|
|
.SS Program source: fanotify_fid.c
|
|
\&
|
|
.EX
|
|
#define _GNU_SOURCE
|
|
#include <errno.h>
|
|
#include <fcntl.h>
|
|
#include <limits.h>
|
|
#include <stdio.h>
|
|
#include <stdlib.h>
|
|
#include <sys/types.h>
|
|
#include <sys/stat.h>
|
|
#include <sys/fanotify.h>
|
|
#include <unistd.h>
|
|
|
|
#define BUF_SIZE 256
|
|
|
|
int
|
|
main(int argc, char **argv)
|
|
{
|
|
int fd, ret, event_fd, mount_fd;
|
|
ssize_t len, path_len;
|
|
char path[PATH_MAX];
|
|
char procfd_path[PATH_MAX];
|
|
char events_buf[BUF_SIZE];
|
|
struct file_handle *file_handle;
|
|
struct fanotify_event_metadata *metadata;
|
|
struct fanotify_event_info_fid *fid;
|
|
const char *file_name;
|
|
struct stat sb;
|
|
|
|
if (argc != 2) {
|
|
fprintf(stderr, "Invalid number of command line arguments.\en");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
mount_fd = open(argv[1], O_DIRECTORY | O_RDONLY);
|
|
if (mount_fd == \-1) {
|
|
perror(argv[1]);
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
|
|
/* Create an fanotify file descriptor with FAN_REPORT_DFID_NAME as
|
|
a flag so that program can receive fid events with directory
|
|
entry name. */
|
|
|
|
fd = fanotify_init(FAN_CLASS_NOTIF | FAN_REPORT_DFID_NAME, 0);
|
|
if (fd == \-1) {
|
|
perror("fanotify_init");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* Place a mark on the filesystem object supplied in argv[1]. */
|
|
|
|
ret = fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_ONLYDIR,
|
|
FAN_CREATE | FAN_ONDIR,
|
|
AT_FDCWD, argv[1]);
|
|
if (ret == \-1) {
|
|
perror("fanotify_mark");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
printf("Listening for events.\en");
|
|
|
|
/* Read events from the event queue into a buffer. */
|
|
|
|
len = read(fd, events_buf, sizeof(events_buf));
|
|
if (len == \-1 && errno != EAGAIN) {
|
|
perror("read");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
/* Process all events within the buffer. */
|
|
|
|
for (metadata = (struct fanotify_event_metadata *) events_buf;
|
|
FAN_EVENT_OK(metadata, len);
|
|
metadata = FAN_EVENT_NEXT(metadata, len)) {
|
|
fid = (struct fanotify_event_info_fid *) (metadata + 1);
|
|
file_handle = (struct file_handle *) fid\->handle;
|
|
|
|
/* Ensure that the event info is of the correct type. */
|
|
|
|
if (fid\->hdr.info_type == FAN_EVENT_INFO_TYPE_FID ||
|
|
fid\->hdr.info_type == FAN_EVENT_INFO_TYPE_DFID) {
|
|
file_name = NULL;
|
|
} else if (fid\->hdr.info_type == FAN_EVENT_INFO_TYPE_DFID_NAME) {
|
|
file_name = file_handle\->f_handle +
|
|
file_handle\->handle_bytes;
|
|
} else {
|
|
fprintf(stderr, "Received unexpected event info type.\en");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
if (metadata\->mask == FAN_CREATE)
|
|
printf("FAN_CREATE (file created):\en");
|
|
|
|
if (metadata\->mask == (FAN_CREATE | FAN_ONDIR))
|
|
printf("FAN_CREATE | FAN_ONDIR (subdirectory created):\en");
|
|
|
|
/* metadata\->fd is set to FAN_NOFD when the group identifies
|
|
objects by file handles. To obtain a file descriptor for
|
|
the file object corresponding to an event you can use the
|
|
struct file_handle that\(aqs provided within the
|
|
fanotify_event_info_fid in conjunction with the
|
|
open_by_handle_at(2) system call. A check for ESTALE is
|
|
done to accommodate for the situation where the file handle
|
|
for the object was deleted prior to this system call. */
|
|
|
|
event_fd = open_by_handle_at(mount_fd, file_handle, O_RDONLY);
|
|
if (event_fd == \-1) {
|
|
if (errno == ESTALE) {
|
|
printf("File handle is no longer valid. "
|
|
"File has been deleted\en");
|
|
continue;
|
|
} else {
|
|
perror("open_by_handle_at");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
}
|
|
|
|
snprintf(procfd_path, sizeof(procfd_path), "/proc/self/fd/%d",
|
|
event_fd);
|
|
|
|
/* Retrieve and print the path of the modified dentry. */
|
|
|
|
path_len = readlink(procfd_path, path, sizeof(path) \- 1);
|
|
if (path_len == \-1) {
|
|
perror("readlink");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
|
|
path[path_len] = \(aq\e0\(aq;
|
|
printf("\etDirectory \(aq%s\(aq has been modified.\en", path);
|
|
|
|
if (file_name) {
|
|
ret = fstatat(event_fd, file_name, &sb, 0);
|
|
if (ret == \-1) {
|
|
if (errno != ENOENT) {
|
|
perror("fstatat");
|
|
exit(EXIT_FAILURE);
|
|
}
|
|
printf("\etEntry \(aq%s\(aq does not exist.\en", file_name);
|
|
} else if ((sb.st_mode & S_IFMT) == S_IFDIR) {
|
|
printf("\etEntry \(aq%s\(aq is a subdirectory.\en", file_name);
|
|
} else {
|
|
printf("\etEntry \(aq%s\(aq is not a subdirectory.\en",
|
|
file_name);
|
|
}
|
|
}
|
|
|
|
/* Close associated file descriptor for this event. */
|
|
|
|
close(event_fd);
|
|
}
|
|
|
|
printf("All events processed successfully. Program exiting.\en");
|
|
exit(EXIT_SUCCESS);
|
|
}
|
|
.EE
|
|
.SH SEE ALSO
|
|
.ad l
|
|
.BR fanotify_init (2),
|
|
.BR fanotify_mark (2),
|
|
.BR inotify (7)
|