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tar: use birthtime rather than ctime when checking identity

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Without this fix, tar would sometimes mishandle the extraction of
hard links to symbolic links.  Problem reported in
<http://lists.gnu.org/archive/html/bug-tar/2011-06/msg00000.html>
by Andreas Stolcke.
* src/extract.c (struct delayed_link): Change ctime member to birthtime.
(same_birthtime): New function.
(create_placeholder_file, extract_link, apply_delayed_links):
Use it to compare birthtimes (when available) instead of ctime.
This commit is contained in:
Paul Eggert
2011-06-07 15:16:55 -07:00
parent 9708b248e8
commit 189e436474
1 changed files with 19 additions and 7 deletions
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26
src/extract.c
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@@ -110,12 +110,15 @@ struct delayed_link
/* The next delayed link in the list. */
struct delayed_link *next;
/* The device, inode number and ctime of the placeholder. Use
ctime, not mtime, to make false matches less likely if some
other process removes the placeholder. */
/* The device, inode number and birthtime of the placeholder.
birthtime.tv_nsec is negative if the birthtime is not available.
Don't use mtime as this would allow for false matches if some
other process removes the placeholder. Don't use ctime as
this would cause race conditions and other screwups, e.g.,
when restoring hard-linked symlinks. */
dev_t dev;
ino_t ino;
struct timespec ctime;
struct timespec birthtime;
/* True if the link is symbolic. */
bool is_symlink;
@@ -268,6 +271,15 @@ set_mode (char const *file_name,
}
}
/* Return true if A and B are the same birthtimes.
Unavailable birthtimes, which have negative tv_nsec members,
all compare equal to each other. */
static bool
same_birthtime (struct timespec a, struct timespec b)
{
return (a.tv_nsec == b.tv_nsec && (a.tv_nsec < 0 || a.tv_sec == b.tv_sec));
}
/* Check time after successfully setting FILE_NAME's time stamp to T. */
static void
check_time (char const *file_name, struct timespec t)
@@ -1076,7 +1088,7 @@ create_placeholder_file (char *file_name, bool is_symlink, bool *interdir_made)
delayed_link_head = p;
p->dev = st.st_dev;
p->ino = st.st_ino;
p->ctime = get_stat_ctime (&st);
p->birthtime = get_stat_birthtime (&st);
p->is_symlink = is_symlink;
if (is_symlink)
{
@@ -1134,7 +1146,7 @@ extract_link (char *file_name, int typeflag)
if (ds->change_dir == chdir_current
&& ds->dev == st1.st_dev
&& ds->ino == st1.st_ino
&& timespec_cmp (ds->ctime, get_stat_ctime (&st1)) == 0)
&& same_birthtime (ds->birthtime, get_stat_birthtime (&st1)))
{
struct string_list *p = xmalloc (offsetof (struct string_list, string)
+ strlen (file_name) + 1);
@@ -1500,7 +1512,7 @@ apply_delayed_links (void)
if (fstatat (chdir_fd, source, &st, AT_SYMLINK_NOFOLLOW) == 0
&& st.st_dev == ds->dev
&& st.st_ino == ds->ino
&& timespec_cmp (get_stat_ctime (&st), ds->ctime) == 0)
&& same_birthtime (get_stat_birthtime (&st), ds->birthtime))
{
/* Unlink the placeholder, then create a hard link if possible,
a symbolic link otherwise. */