On Tue, Dec 11, 2012 at 08:56:16AM -0500, Jeff Layton wrote: > When path_init is called with a valid dfd, that code checks permissions > on the open directory fd and returns an error if the check fails. This > permission check is redundant, however. > > Both callers of path_init immediately call link_path_walk afterward. The > first thing that link_path_walk does is to check for exec permissions > at the starting point of the path walk. > > In most cases, these checks are very quick, but when the dfd is for a > file on a NFS mount with the actimeo=0, each permission check goes > out onto the wire. The result is 2 identical ACCESS calls. > > Given that these codepaths are fairly "hot", I think it makes sense to > eliminate the permission check in path_init and simply assume that the > caller will eventually check the permissions before proceeding. Applied, with one modification to commit message - the second paragraph replaced with Both callers of path_init immediately call link_path_walk afterward. The first thing that link_path_walk does for pathnames that do not consist only of slashes is to check for exec permissions at the starting point of the path walk. And this check in path_init() is on the path taken only when *name != '/' && *name != '\0'. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
