mirror of https://github.com/mkerrisk/man-pages
ftw.3: Reorganize the page to give primacy to nftw()
nftw() is the better API, and POSIX.1-2008 marks ftw() obsolete. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk
parent
3591ce3e19
commit
d954cea8fd
246
man3/ftw.3
246
man3/ftw.3
|
|
@ -33,31 +33,35 @@
|
|||
.\" 2006-05-24, Michael Kerrisk <mtk.manpages@gmail.com>
|
||||
.\" Added an example program.
|
||||
.\"
|
||||
.\" FIXME: This page should be rewritten to first of all describe
|
||||
.\" nftw() and then describe the differnces in the older ftw().
|
||||
.\"
|
||||
.TH FTW 3 2014-12-31 "Linux" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
ftw, nftw \- file tree walk
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <ftw.h>
|
||||
.sp
|
||||
.BI "int ftw(const char *" dirpath ,
|
||||
.BI " int (*" fn ") (const char *" fpath ", const struct stat *" sb ,
|
||||
.BI " int " typeflag ),
|
||||
.BI " int " nopenfd );
|
||||
.sp
|
||||
.BR "#define _XOPEN_SOURCE 500" " /* See feature_test_macros(7) */"
|
||||
.B #include <ftw.h>
|
||||
.sp
|
||||
|
||||
.BI "int nftw(const char *" dirpath ,
|
||||
.BI " int (*" fn ") (const char *" fpath ", const struct stat *" sb ,
|
||||
.BI " int " typeflag ", struct FTW *" ftwbuf ),
|
||||
.BI " int " nopenfd ", int " flags );
|
||||
|
||||
.B #include <ftw.h>
|
||||
|
||||
.BI "int ftw(const char *" dirpath ,
|
||||
.BI " int (*" fn ") (const char *" fpath ", const struct stat *" sb ,
|
||||
.BI " int " typeflag ),
|
||||
.BI " int " nopenfd );
|
||||
.fi
|
||||
.sp
|
||||
.in -4n
|
||||
Feature Test Macro Requirements for glibc (see
|
||||
.BR feature_test_macros (7)):
|
||||
.in
|
||||
.sp
|
||||
.BR nftw ():
|
||||
_XOPEN_SOURCE >= 500
|
||||
.SH DESCRIPTION
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
walks through the directory tree that is
|
||||
located under the directory \fIdirpath\fP,
|
||||
and calls \fIfn\fP() once for each entry in the tree.
|
||||
|
|
@ -66,30 +70,31 @@ subdirectories they contain (preorder traversal).
|
|||
|
||||
To avoid using up all of the calling process's file descriptors,
|
||||
\fInopenfd\fP specifies the maximum number of directories that
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
will hold open simultaneously.
|
||||
When
|
||||
the search depth exceeds this,
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
will become slower because
|
||||
directories have to be closed and reopened.
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
uses at most
|
||||
one file descriptor for each level in the directory tree.
|
||||
|
||||
For each entry found in the tree,
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
calls
|
||||
\fIfn\fP() with three arguments:
|
||||
\fIfn\fP() with four arguments:
|
||||
.IR fpath ,
|
||||
.IR sb ,
|
||||
.IR typeflag ,
|
||||
and
|
||||
.IR typeflag .
|
||||
.IR ftwbuf .
|
||||
.I fpath
|
||||
is the pathname of the entry,
|
||||
and is expressed either as a pathname relative to the calling process's
|
||||
current working directory at the time of the call to
|
||||
.BR ftw (),
|
||||
.BR nftw (),
|
||||
if
|
||||
.IR dirpath
|
||||
was expressed as a relative pathname,
|
||||
|
|
@ -118,6 +123,20 @@ is a directory.
|
|||
.I fpath
|
||||
is a directory which can't be read.
|
||||
.TP
|
||||
.B FTW_DP
|
||||
.I fpath
|
||||
is a directory, and \fBFTW_DEPTH\fP was specified in \fIflags\fP.
|
||||
(If
|
||||
.B FTW_DEPTH
|
||||
was not specified in
|
||||
.IR flags ,
|
||||
then directories will always be visited with
|
||||
.I typeflag
|
||||
set to
|
||||
.BR FTW_D .)
|
||||
All of the files
|
||||
and subdirectories within \fIfpath\fP have been processed.
|
||||
.TP
|
||||
.B FTW_NS
|
||||
The
|
||||
.BR stat (2)
|
||||
|
|
@ -131,27 +150,54 @@ could be seen,
|
|||
but did not have execute permission,
|
||||
so that the file could not be reached for
|
||||
.BR stat (2).
|
||||
.sp
|
||||
If
|
||||
.TP
|
||||
.B FTW_SL
|
||||
.I fpath
|
||||
is a symbolic link and
|
||||
.BR stat (2)
|
||||
failed, POSIX.1-2008 states
|
||||
that it is undefined whether \fBFTW_NS\fP or \fBFTW_SL\fP (see below)
|
||||
is passed in
|
||||
.IR typeflag .
|
||||
(For the more modern
|
||||
.BR nftw (),
|
||||
described below,
|
||||
the bahavior is defined:
|
||||
.BR FTW_NS
|
||||
is returned for this case.)
|
||||
is a symbolic link, and \fBFTW_PHYS\fP was set in \fIflags\fP.
|
||||
.\" To obtain the definition of this constant from
|
||||
.\" .IR <ftw.h> ,
|
||||
.\" either
|
||||
.\" .B _BSD_SOURCE
|
||||
.\" must be defined, or
|
||||
.\" .BR _XOPEN_SOURCE
|
||||
.\" must be defined with a value of 500 or more.
|
||||
.TP
|
||||
.B FTW_SLN
|
||||
.I fpath
|
||||
is a symbolic link pointing to a nonexistent file.
|
||||
(This occurs only if \fBFTW_PHYS\fP is not set.)
|
||||
.PP
|
||||
The fourth argument that
|
||||
.BR nftw ()
|
||||
supplies when calling
|
||||
\fIfn\fP()
|
||||
is a structure of type \fIFTW\fP:
|
||||
.in +4n
|
||||
.nf
|
||||
|
||||
struct FTW {
|
||||
int base;
|
||||
int level;
|
||||
};
|
||||
|
||||
.fi
|
||||
.in
|
||||
.I base
|
||||
is the offset of the filename (i.e., basename component)
|
||||
in the pathname given in
|
||||
.IR fpath .
|
||||
.I level
|
||||
is the depth of
|
||||
.I fpath
|
||||
in the directory tree, relative to the root of the tree
|
||||
.RI ( dirpath ,
|
||||
which has depth 0).
|
||||
.PP
|
||||
To stop the tree walk, \fIfn\fP() returns a nonzero value; this
|
||||
value will become the return value of
|
||||
.BR ftw ().
|
||||
.BR nftw ().
|
||||
As long as \fIfn\fP() returns 0,
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
will continue either until it has traversed the entire tree,
|
||||
in which case it will return zero,
|
||||
or until it encounters an error (such as a
|
||||
|
|
@ -159,7 +205,7 @@ or until it encounters an error (such as a
|
|||
failure), in which case it will return \-1.
|
||||
.PP
|
||||
Because
|
||||
.BR ftw ()
|
||||
.BR nftw ()
|
||||
uses dynamic data structures, the only safe way to
|
||||
exit out of a tree walk is to return a nonzero value from \fIfn\fP().
|
||||
To allow a signal to terminate the walk without causing a memory leak,
|
||||
|
|
@ -167,15 +213,10 @@ have the handler set a global flag that is checked by \fIfn\fP().
|
|||
\fIDon't\fP use
|
||||
.BR longjmp (3)
|
||||
unless the program is going to terminate.
|
||||
.SS nftw()
|
||||
The function
|
||||
.BR nftw ()
|
||||
is the same as
|
||||
.BR ftw (),
|
||||
except that it has one additional argument, \fIflags\fP,
|
||||
and calls \fIfn\fP() with one more argument, \fIftwbuf\fP.
|
||||
|
||||
This \fIflags\fP argument is formed by ORing zero or more of the
|
||||
The \fIflags\fP argument of
|
||||
.BR nftw ()
|
||||
is formed by ORing zero or more of the
|
||||
following flags:
|
||||
.TP
|
||||
.BR FTW_ACTIONRETVAL " (since glibc 2.3.3)"
|
||||
|
|
@ -258,77 +299,37 @@ If \fBFTW_PHYS\fP is not set, but \fBFTW_DEPTH\fP is set,
|
|||
then the function
|
||||
.IR fn ()
|
||||
is never called for a directory that would be a descendant of itself.
|
||||
.LP
|
||||
For each entry in the directory tree,
|
||||
.SS ftw()
|
||||
.BR ftw ()
|
||||
is an older function that offers a subset of the functionality of
|
||||
.BR nftw ().
|
||||
The notable differences are as follows:
|
||||
.IP * 3
|
||||
.BR ftw ()
|
||||
has no
|
||||
.IR flags
|
||||
argument.
|
||||
It behaves the same as when
|
||||
.BR nftw ()
|
||||
calls
|
||||
is called with
|
||||
.I flags
|
||||
specified as zero.
|
||||
.IP *
|
||||
The callback function,
|
||||
.IR fn (),
|
||||
is not supplied with a fourth argument.
|
||||
.IP *
|
||||
The range of values that is passed via the
|
||||
.I typeflag
|
||||
argument supplied to
|
||||
.IR fn ()
|
||||
with four arguments.
|
||||
.I fpath
|
||||
and
|
||||
.I sb
|
||||
are as for
|
||||
.BR ftw ().
|
||||
.I typeflag
|
||||
may receive any of the same values as with
|
||||
.BR ftw (),
|
||||
or any of the following values:
|
||||
.TP
|
||||
.B FTW_DP
|
||||
.I fpath
|
||||
is a directory, and \fBFTW_DEPTH\fP was specified in \fIflags\fP.
|
||||
(If
|
||||
.B FTW_DEPTH
|
||||
was not specified in
|
||||
.IR flags ,
|
||||
then directories will always be visited with
|
||||
.I typeflag
|
||||
set to
|
||||
.BR FTW_D .)
|
||||
All of the files
|
||||
and subdirectories within \fIfpath\fP have been processed.
|
||||
.TP
|
||||
.B FTW_SL
|
||||
.I fpath
|
||||
is a symbolic link, and \fBFTW_PHYS\fP was set in \fIflags\fP.
|
||||
.\" To obtain the definition of this constant from
|
||||
.\" .IR <ftw.h> ,
|
||||
.\" either
|
||||
.\" .B _BSD_SOURCE
|
||||
.\" must be defined, or
|
||||
.\" .BR _XOPEN_SOURCE
|
||||
.\" must be defined with a value of 500 or more.
|
||||
.TP
|
||||
.B FTW_SLN
|
||||
.I fpath
|
||||
is a symbolic link pointing to a nonexistent file.
|
||||
(This occurs only if \fBFTW_PHYS\fP is not set.)
|
||||
.LP
|
||||
The fourth argument that
|
||||
.BR nftw ()
|
||||
supplies when calling
|
||||
\fIfn\fP()
|
||||
is a structure of type \fIFTW\fP:
|
||||
.in +4n
|
||||
.nf
|
||||
|
||||
struct FTW {
|
||||
int base;
|
||||
int level;
|
||||
};
|
||||
|
||||
.fi
|
||||
.in
|
||||
.I base
|
||||
is the offset of the filename (i.e., basename component)
|
||||
in the pathname given in
|
||||
.IR fpath .
|
||||
.I level
|
||||
is the depth of
|
||||
.I fpath
|
||||
in the directory tree, relative to the root of the tree
|
||||
.RI ( dirpath ,
|
||||
which has depth 0).
|
||||
is smaller: just
|
||||
.BR FTW_F ,
|
||||
.BR FTW_D ,
|
||||
.BR FTW_DNR ,
|
||||
.BR FTW_NS ,
|
||||
and (possibly)
|
||||
.BR FTW_SL .
|
||||
.SH RETURN VALUE
|
||||
These functions return 0 on success, and \-1 if an error occurs.
|
||||
|
||||
|
|
@ -365,20 +366,23 @@ and the use of \fBFTW_SL\fP with
|
|||
.BR ftw ()
|
||||
were introduced in SUSv1.
|
||||
.LP
|
||||
On some systems
|
||||
In some implementations (e.g., glibc),
|
||||
.BR ftw ()
|
||||
will never use \fBFTW_SL\fP, on other systems \fBFTW_SL\fP occurs only
|
||||
for symbolic links that do not point to an existing file,
|
||||
and again on other systems
|
||||
.BR ftw ()
|
||||
will use \fBFTW_SL\fP for each symbolic link.
|
||||
For predictable control, use
|
||||
If
|
||||
.I fpath
|
||||
is a symbolic link and
|
||||
.BR stat (2)
|
||||
failed, POSIX.1-2008 states
|
||||
that it is undefined whether \fBFTW_NS\fP or \fBFTW_SL\fP
|
||||
is passed in
|
||||
.IR typeflag .
|
||||
For predictable results, use
|
||||
.BR nftw ().
|
||||
.LP
|
||||
\fBFTW_F\fP is returned for all objects (files, symbolic links, FIFOs, etc.)
|
||||
that can be stat'ed but are not a directory.
|
||||
|
||||
\fBFTW_ACTIONRETVAL\fP is glibc-specific.
|
||||
.SH EXAMPLE
|
||||
The following program traverses the directory tree under the path named
|
||||
in its first command-line argument, or under the current directory
|
||||
|
|
|
|||
Loading…
Reference in New Issue