mirror of https://github.com/mkerrisk/man-pages
Consistent use of terms "open file description",
"file status flags", and "file decriptor flags" Some rewriting of discussion of file descriptor flags Under F_DUPFD, replaced some text duplicated in dup.2 with a cross ref to dup.2 Minor wording and formatting fixes
This commit is contained in:
Michael Kerrisk
parent
0a5a85eb64
commit
cff88e99ab
77
man2/fcntl.2
77
man2/fcntl.2
|
|
@ -66,12 +66,12 @@ fcntl \- manipulate file descriptor
|
|||
.BI "int fcntl(int " fd ", int " cmd ", struct flock *" lock );
|
||||
.fi
|
||||
.SH DESCRIPTION
|
||||
.B fcntl
|
||||
performs one of various miscellaneous operations on
|
||||
.BR fcntl ()
|
||||
performs one of the operations described below on the open file descriptor
|
||||
.IR fd .
|
||||
The operation in question is determined by
|
||||
The operation is determined by
|
||||
.IR cmd .
|
||||
.SS "Handling close-on-exec"
|
||||
.SS "Duplicating a file descriptor"
|
||||
.TP
|
||||
.B F_DUPFD
|
||||
Find the lowest numbered available file descriptor
|
||||
|
|
@ -79,57 +79,62 @@ greater than or equal to
|
|||
.I arg
|
||||
and make it be a copy of
|
||||
.IR fd .
|
||||
This is different form
|
||||
This is different from
|
||||
.BR dup2 (2)
|
||||
which uses exactly the descriptor specified.
|
||||
.sp
|
||||
The old and new descriptors may be used interchangeably. They share locks,
|
||||
file position pointers and flags; for example, if the file position is
|
||||
modified by using
|
||||
.B lseek
|
||||
on one of the descriptors, the position is also changed for the other.
|
||||
.sp
|
||||
The two descriptors do not share the close-on-exec flag, however.
|
||||
The close-on-exec flag of the copy is off, meaning that it will
|
||||
not be closed on exec.
|
||||
.sp
|
||||
On success, the new descriptor is returned.
|
||||
.TP
|
||||
.B F_GETFD
|
||||
Read the close-on-exec flag. If the
|
||||
.sp
|
||||
See
|
||||
.BR dup (2)
|
||||
for further details.
|
||||
.SS "The file descriptor flags"
|
||||
The following commands manipulate the flags associated with
|
||||
a file descriptor.
|
||||
Currently, only one such flag is defined:
|
||||
.BR FD_CLOEXEC ,
|
||||
the close-on-exec flag.
|
||||
If the
|
||||
.B FD_CLOEXEC
|
||||
bit is 0, the file will remain open across
|
||||
.BR exec ,
|
||||
bit is 0, the file descriptor will remain open across an
|
||||
.BR execve (2),
|
||||
otherwise it will be closed.
|
||||
.TP
|
||||
.B F_GETFD
|
||||
Read the file descriptor flags.
|
||||
.TP
|
||||
.B F_SETFD
|
||||
Set the close-on-exec flag to the value specified by the
|
||||
.B FD_CLOEXEC
|
||||
bit of
|
||||
Set the file descriptor flags to the value specified by
|
||||
.IR arg .
|
||||
.SS "The file status flags"
|
||||
A file descriptor has certain associated flags, initialized by
|
||||
Each open file description has certain associated flags, initialized by
|
||||
.BR open (2)
|
||||
.\" or
|
||||
.\" .BR creat (2),
|
||||
and possibly modified by
|
||||
.BR fcntl (2).
|
||||
The flags are shared between copies (made with
|
||||
.BR dup (2),
|
||||
.BR fork (2),
|
||||
etc.) of the same file descriptor.
|
||||
Duplicated file descriptors
|
||||
(made with
|
||||
.BR dup (),
|
||||
.BR fcntl (F_DUPFD),
|
||||
.BR fork (),
|
||||
etc.) refer to the same open file description, and thus
|
||||
share the same file status flags.
|
||||
.sp
|
||||
The flags and their semantics are described in
|
||||
The file status flags and their semantics are described in
|
||||
.BR open (2).
|
||||
.TP
|
||||
.B F_GETFL
|
||||
Read the file descriptor's flags.
|
||||
Read the file status flags.
|
||||
.TP
|
||||
.B F_SETFL
|
||||
Set the file status flags part of the descriptor's flags to the value
|
||||
specified by
|
||||
Set the file status flags to the value specified by
|
||||
.IR arg .
|
||||
Remaining bits (access mode, file creation flags) in
|
||||
File access mode
|
||||
.RB ( O_RDONLY ", " O_WRONLY ", " O_RDWR )
|
||||
and file creation flags
|
||||
.RB ( O_CREAT ", " O_EXCL ", " O_NOCTTY ", " O_TRUNC )
|
||||
in
|
||||
.I arg
|
||||
are ignored.
|
||||
On Linux this command can only change the
|
||||
|
|
@ -365,7 +370,7 @@ status flag on a file descriptor (either by providing this flag with the
|
|||
call, or by using the
|
||||
.B F_SETFL
|
||||
command of
|
||||
.BR fcntl ),
|
||||
.BR fcntl ()),
|
||||
a SIGIO signal is sent whenever input or output becomes possible
|
||||
on that file descriptor.
|
||||
.B F_SETSIG
|
||||
|
|
@ -405,7 +410,7 @@ If a non-zero value is given to
|
|||
.B F_SETSIG
|
||||
in a multi-threaded process running with a threading library
|
||||
that supports thread groups (e.g., NPTL),
|
||||
then a positive value value given to
|
||||
then a positive value given to
|
||||
.B F_SETOWN
|
||||
has a different meaning:
|
||||
.\" The relevant place in the (2.6) kernel source is the
|
||||
|
|
@ -790,7 +795,7 @@ Attempted to clear the
|
|||
flag on a file that has the append-only attribute set.
|
||||
.SH NOTES
|
||||
The errors returned by
|
||||
.B dup2
|
||||
.BR dup2 ()
|
||||
are different from those returned by
|
||||
.BR F_DUPFD .
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue