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ftw.3: glibc eventually fixed a regression in FTW_SLN behavior 

For details, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1422736
http://austingroupbugs.net/view.php?id=1121
https://bugzilla.redhat.com/show_bug.cgi?id=1422736

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2020-04-28 13:17:06 +02:00
parent 2ece4ef7c6
commit 518271052d
1 changed files with 21 additions and 33 deletions
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54
man3/ftw.3
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@ -173,14 +173,14 @@ is a symbolic link, and \fBFTW_PHYS\fP was set in \fIflags\fP.
.I fpath
is a symbolic link pointing to a nonexistent file.
(This occurs only if \fBFTW_PHYS\fP is not set.)
On most implementations, in this case the
In this case the
.I sb
argument passed to
.IR fn ()
contains information returned by performing
.BR lstat (2)
on the symbolic link.
For the details on Linux, see BUGS.
on the "dangling" symbolic link.
(But see BUGS.)
.PP
The fourth argument
.RI ( ftwbuf )
@ -417,44 +417,32 @@ is passed in
For predictable results, use
.BR nftw ().
.SH BUGS
In the specification of
.BR nftw (),
POSIX.1 notes that when
.B FTW_NS
is passed as the
.I typeflag
argument of
.IR fn (),
then the contents of the buffer pointed to by the
According to POSIX.1-2008, when the
.IR typeflag
argument passed to
.IR fn ()
contains
.BR FTW_SLN ,
the buffer pointed to by
.I sb
argument are undefined.
The standard makes no such statement for the case where
.B FTW_SLN
is passed in
.IR typeflag ,
with the implication that the contents of the buffer pointed to by
.I sb
are defined.
And indeed this is the case on most implementations: the buffer pointed to by
.I sb
contains the results produced by applying
should contain information about the dangling symbolic link
(obtained by calling
.BR lstat (2)
to the symbolic link.
In early glibc, the behavior was the same.
However, since glibc 2.4, the contents of the buffer pointed to by
on the link).
Early glibc versions correctly followed the POSIX specification on this point.
However, as a result of a regression introduced in glibc 2.4,
the contents of the buffer pointed to by
.I sb
are undefined when
were undefined when
.B FTW_SLN
is passed in
.IR typeflag .
This change
.I appears
to be an unintended regression,
but it is not (yet) clear if the behavior will be restored to that
provided in the original glibc implementation (and on other implementations).
.\" FIXME .
(More precisely, the contents of the buffer were left unchanged in this case.)
This regression was eventually fixed in glibc 2.30,
.\" https://bugzilla.redhat.com/show_bug.cgi?id=1422736
.\" http://austingroupbugs.net/view.php?id=1121
.\" https://bugzilla.redhat.com/show_bug.cgi?id=1422736
so that the glibc implementation (once more) follows the POSIX specification.
.SH EXAMPLE
The following program traverses the directory tree under the path named
in its first command-line argument, or under the current directory