From 45c9b11a1d07770cabb48cb0f7960a77650ffc64 Mon Sep 17 00:00:00 2001 From: Ulrich Drepper Date: Sun, 25 Jun 2006 05:49:11 -0700 Subject: [PATCH] [PATCH] Implement AT_SYMLINK_FOLLOW flag for linkat 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 Acked-by: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/namei.c | 6 ++++-- include/linux/fcntl.h | 1 + 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index bb4a3e40e4..c784e8bb57 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2243,14 +2243,16 @@ asmlinkage long sys_linkat(int olddfd, const char __user *oldname, 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); diff --git a/include/linux/fcntl.h b/include/linux/fcntl.h index c52a63755f..996f5611cd 100644 --- a/include/linux/fcntl.h +++ b/include/linux/fcntl.h @@ -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__ -- 2.39.5