Messages in this thread Patch in this message | | | Date | Sat, 17 Jun 2006 15:13:22 -0400 | From | Ulrich Drepper <> | Subject | [PATCH] Implement AT_SYMLINK_FOLLOW flag for linkat |
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When the linkat() syscall was added the flag parameter was added in the last minute but it wasn't used so far. The following patch should change that. My tests show that this is all that's needed.
If OLDNAME is a symlink setting the flag causes linkat to follow the symlink and create a hardlink with the target. This is actually the behavior POSIX demands for link() as well but Linux wisely does not do this. With this flag (which will most likely be in the next POSIX revision) the programmer can choose the behavior, defaulting to the safe variant. As a side effect it is now possible to implement a POSIX-compliant link(2) function for those who are interested.
touch file ln -s file symlink
linkat(fd, "symlink", fd, "newlink", 0) -> newlink is hardlink of symlink
linkat(fd, "symlink", fd, "newlink", AT_SYMLINK_FOLLOW) -> newlink is hardlink of file
The value of AT_SYMLINK_FOLLOW is determined by the definition we already use in glibc.
Signed-Off-By: Ulrich Drepper <drepper@redhat.com>
fs/namei.c | 6 ++++-- include/linux/fcntl.h | 1 + 2 files changed, 5 insertions(+), 2 deletions(-)
--- linux/fs/namei.c-follow 2006-06-17 11:22:39.000000000 -0700 +++ linux/fs/namei.c 2006-06-17 11:58:18.000000000 -0700 @@ -2243,14 +2243,16 @@ int error; char * to; - if (flags != 0) + if ((flags & ~AT_SYMLINK_FOLLOW) != 0) return -EINVAL; to = getname(newname); if (IS_ERR(to)) return PTR_ERR(to); - error = __user_walk_fd(olddfd, oldname, 0, &old_nd); + error = __user_walk_fd(olddfd, oldname, + flags & AT_SYMLINK_FOLLOW ? LOOKUP_FOLLOW : 0, + &old_nd); if (error) goto exit; error = do_path_lookup(newdfd, to, LOOKUP_PARENT, &nd); --- linux/include/linux/fcntl.h-follow 2006-06-17 11:24:21.000000000 -0700 +++ linux/include/linux/fcntl.h 2006-06-17 11:24:51.000000000 -0700 @@ -29,6 +29,7 @@ #define AT_SYMLINK_NOFOLLOW 0x100 /* Do not follow symbolic links. */ #define AT_REMOVEDIR 0x200 /* Remove directory instead of unlinking file. */ +#define AT_SYMLINK_FOLLOW 0x400 /* Follow symbolic links. */ #ifdef __KERNEL__ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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