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cp, mv: use linkat to guarantee semantics

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* src/copy.c (copy_internal): Use linkat, not link.
This commit is contained in:
Eric Blake
2009-09-24 17:11:26 -06:00
parent efcee783e4
commit ca9e212cf8
1 changed files with 11 additions and 18 deletions
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29
src/copy.c
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@@ -1687,7 +1687,9 @@ copy_internal (char const *src_name, char const *dst_name,
}
else
{
bool link_failed = (link (earlier_file, dst_name) != 0);
/* We want to guarantee that symlinks are not followed. */
bool link_failed = (linkat (AT_FDCWD, earlier_file, AT_FDCWD,
dst_name, 0) != 0);
/* If the link failed because of an existing destination,
remove that file and then call link again. */
@@ -1700,7 +1702,8 @@ copy_internal (char const *src_name, char const *dst_name,
}
if (x->verbose)
printf (_("removed %s\n"), quote (dst_name));
link_failed = (link (earlier_file, dst_name) != 0);
link_failed = (linkat (AT_FDCWD, earlier_file, AT_FDCWD,
dst_name, 0) != 0);
}
if (link_failed)
@@ -1990,25 +1993,15 @@ copy_internal (char const *src_name, char const *dst_name,
}
}
/* POSIX 2008 states that it is implementation-defined whether
link() on a symlink creates a hard-link to the symlink, or only
to the referent (effectively dereferencing the symlink) (POSIX
2001 required the latter behavior, although many systems provided
the former). Yet cp, invoked with `--link --no-dereference',
should not follow the link. We can approximate the desired
behavior by skipping this hard-link creating block and instead
copying the symlink, via the `S_ISLNK'- copying code below.
LINK_FOLLOWS_SYMLINKS is tri-state; if it is -1, we don't know
how link() behaves, so we use the fallback case for safety.
FIXME - use a gnulib linkat emulation for more fine-tuned
emulation, particularly when LINK_FOLLOWS_SYMLINKS is -1. */
/* cp, invoked with `--link --no-dereference', should not follow the
link; we guarantee this with gnulib's linkat module (on systems
where link(2) follows the link, gnulib creates a symlink with
identical contents, which is good enough for our purposes). */
else if (x->hard_link
&& (!LINK_FOLLOWS_SYMLINKS
|| !S_ISLNK (src_mode)
&& (!S_ISLNK (src_mode)
|| x->dereference != DEREF_NEVER))
{
if (link (src_name, dst_name))
if (linkat (AT_FDCWD, src_name, AT_FDCWD, dst_name, 0))
{
error (0, errno, _("cannot create link %s"), quote (dst_name));
goto un_backup;