user/sven/linux.git/include/linux/namei.h, branch v3.0.61

vfs pathname lookup: Add LOOKUP_AUTOMOUNT flag

2011-11-11T17:36:23Z

Since we've now turned around and made LOOKUP_FOLLOW *not* force an automount, we want to add the ability to force an automount event on lookup even if we don't happen to have one of the other flags that force it implicitly (LOOKUP_OPEN, LOOKUP_DIRECTORY, LOOKUP_PARENT..) Most cases will never want to use this, since you'd normally want to delay automounting as long as possible, which usually implies LOOKUP_OPEN (when we open a file or directory, we really cannot avoid the automount any more). But Trond argued sufficiently forcefully that at a minimum bind mounting a file and quotactl will want to force the automount lookup. Some other cases (like nfs_follow_remote_path()) could use it too, although LOOKUP_DIRECTORY would work there as well. This commit just adds the flag and logic, no users yet, though. It also doesn't actually touch the LOOKUP_NO_AUTOMOUNT flag that is related, and was made irrelevant by the same change that made us not follow on LOOKUP_FOLLOW. Cc: Trond Myklebust Cc: Ian Kent Cc: Jeff Layton Cc: Miklos Szeredi Cc: David Howells Cc: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Miklos Szeredi Signed-off-by: Greg Kroah-Hartman

readlinkat: ensure we return ENOENT for the empty pathname for normal lookups

2011-11-11T17:36:19Z

commit 1fa1e7f615f4d3ae436fa319af6e4eebdd4026a8 upstream. Since the commit below which added O_PATH support to the *at() calls, the error return for readlink/readlinkat for the empty pathname has switched from ENOENT to EINVAL: commit 65cfc6722361570bfe255698d9cd4dccaf47570d Author: Al Viro Date: Sun Mar 13 15:56:26 2011 -0400 readlinkat(), fchownat() and fstatat() with empty relative pathnames This is both unexpected for userspace and makes readlink/readlinkat inconsistant with all other interfaces; and inconsistant with our stated return for these pathnames. As the readlinkat call does not have a flags parameter we cannot use the AT_EMPTY_PATH approach used in the other calls. Therefore expose whether the original path is infact entry via a new user_path_at_empty() path lookup function. Use this to determine whether to default to EINVAL or ENOENT for failures. Addresses http://bugs.launchpad.net/bugs/817187 [akpm@linux-foundation.org: remove unused getname_flags()] Signed-off-by: Andy Whitcroft Cc: Christoph Hellwig Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Christoph Hellwig Signed-off-by: Greg Kroah-Hartman

don't pass 'mounting_here' flag to follow_down()

2011-03-18T13:04:20Z

it's always false now Signed-off-by: Al Viro

New AT_... flag: AT_EMPTY_PATH

2011-03-14T23:12:20Z

For name_to_handle_at(2) we'll want both ...at()-style syscall that would be usable for non-directory descriptors (with empty relative pathname). Introduce new flag (AT_EMPTY_PATH) to deal with that and corresponding LOOKUP_EMPTY; teach user_path_at() and path_init() to deal with the latter. Signed-off-by: Al Viro

reduce vfs_path_lookup() to do_path_lookup()

2011-03-14T13:15:27Z

New lookup flag: LOOKUP_ROOT. nd->root is set (and held) by caller, path_init() starts walking from that place and all pathname resolution machinery never drops nd->root if that flag is set. That turns vfs_path_lookup() into a special case of do_path_lookup() *and* gets us down to 3 callers of link_path_walk(), making it finally feasible to rip the handling of trailing symlink out of link_path_walk(). That will not only simply the living hell out of it, but make life much simpler for unionfs merge. Trailing symlink handling will become iterative, which is a good thing for stack footprint in a lot of situations as well. Signed-off-by: Al Viro

get rid of nd->file

2011-03-14T13:15:26Z

Don't stash the struct file * used as starting point of walk in nameidata; pass file ** to path_init() instead. Signed-off-by: Al Viro

untangle the "need_reval_dot" mess

2011-03-14T13:15:24Z

instead of ad-hackery around need_reval_dot(), do the following: set a flag (LOOKUP_JUMPED) in the beginning of path, on absolute symlink traversal, on ".." and on procfs-style symlinks. Clear on normal components, leave unchanged on ".". Non-nested callers of link_path_walk() call handle_reval_path(), which checks that flag is set and that fs does want the final revalidate thing, then does ->d_revalidate(). In link_path_walk() all the return_reval stuff is gone. Signed-off-by: Al Viro

kill path_lookup()

2011-03-14T13:15:23Z

all remaining callers pass LOOKUP_PARENT to it, so flags argument can die; renamed to kern_path_parent() Signed-off-by: Al Viro

Add an AT_NO_AUTOMOUNT flag to suppress terminal automount

2011-01-16T01:07:33Z

Add an AT_NO_AUTOMOUNT flag to suppress terminal automounting of automount point directories. This can be used by fstatat() users to permit the gathering of attributes on an automount point and also prevent mass-automounting of a directory of automount points by ls. Signed-off-by: David Howells Acked-by: Ian Kent Signed-off-by: Al Viro

Add a dentry op to allow processes to be held during pathwalk transit

2011-01-16T01:07:31Z

Add a dentry op (d_manage) to permit a filesystem to hold a process and make it sleep when it tries to transit away from one of that filesystem's directories during a pathwalk. The operation is keyed off a new dentry flag (DCACHE_MANAGE_TRANSIT). The filesystem is allowed to be selective about which processes it holds and which it permits to continue on or prohibits from transiting from each flagged directory. This will allow autofs to hold up client processes whilst letting its userspace daemon through to maintain the directory or the stuff behind it or mounted upon it. The ->d_manage() dentry operation: int (*d_manage)(struct path *path, bool mounting_here); takes a pointer to the directory about to be transited away from and a flag indicating whether the transit is undertaken by do_add_mount() or do_move_mount() skipping through a pile of filesystems mounted on a mountpoint. It should return 0 if successful and to let the process continue on its way; -EISDIR to prohibit the caller from skipping to overmounted filesystems or automounting, and to use this directory; or some other error code to return to the user. ->d_manage() is called with namespace_sem writelocked if mounting_here is true and no other locks held, so it may sleep. However, if mounting_here is true, it may not initiate or wait for a mount or unmount upon the parameter directory, even if the act is actually performed by userspace. Within fs/namei.c, follow_managed() is extended to check with d_manage() first on each managed directory, before transiting away from it or attempting to automount upon it. follow_down() is renamed follow_down_one() and should only be used where the filesystem deliberately intends to avoid management steps (e.g. autofs). A new follow_down() is added that incorporates the loop done by all other callers of follow_down() (do_add/move_mount(), autofs and NFSD; whilst AFS, NFS and CIFS do use it, their use is removed by converting them to use d_automount()). The new follow_down() calls d_manage() as appropriate. It also takes an extra parameter to indicate if it is being called from mount code (with namespace_sem writelocked) which it passes to d_manage(). follow_down() ignores automount points so that it can be used to mount on them. __follow_mount_rcu() is made to abort rcu-walk mode if it hits a directory with DCACHE_MANAGE_TRANSIT set on the basis that we're probably going to have to sleep. It would be possible to enter d_manage() in rcu-walk mode too, and have that determine whether to abort or not itself. That would allow the autofs daemon to continue on in rcu-walk mode. Note that DCACHE_MANAGE_TRANSIT on a directory should be cleared when it isn't required as every tranist from that directory will cause d_manage() to be invoked. It can always be set again when necessary. ========================== WHAT THIS MEANS FOR AUTOFS ========================== Autofs currently uses the lookup() inode op and the d_revalidate() dentry op to trigger the automounting of indirect mounts, and both of these can be called with i_mutex held. autofs knows that the i_mutex will be held by the caller in lookup(), and so can drop it before invoking the daemon - but this isn't so for d_revalidate(), since the lock is only held on _some_ of the code paths that call it. This means that autofs can't risk dropping i_mutex from its d_revalidate() function before it calls the daemon. The bug could manifest itself as, for example, a process that's trying to validate an automount dentry that gets made to wait because that dentry is expired and needs cleaning up: mkdir S ffffffff8014e05a 0 32580 24956 Call Trace: [] :autofs4:autofs4_wait+0x674/0x897 [] avc_has_perm+0x46/0x58 [] autoremove_wake_function+0x0/0x2e [] :autofs4:autofs4_expire_wait+0x41/0x6b [] :autofs4:autofs4_revalidate+0x91/0x149 [] __lookup_hash+0xa0/0x12f [] lookup_create+0x46/0x80 [] sys_mkdirat+0x56/0xe4 versus the automount daemon which wants to remove that dentry, but can't because the normal process is holding the i_mutex lock: automount D ffffffff8014e05a 0 32581 1 32561 Call Trace: [] __mutex_lock_slowpath+0x60/0x9b [] do_path_lookup+0x2ca/0x2f1 [] .text.lock.mutex+0xf/0x14 [] do_rmdir+0x77/0xde [] tracesys+0x71/0xe0 [] tracesys+0xd5/0xe0 which means that the system is deadlocked. This patch allows autofs to hold up normal processes whilst the daemon goes ahead and does things to the dentry tree behind the automouter point without risking a deadlock as almost no locks are held in d_manage() and none in d_automount(). Signed-off-by: David Howells Was-Acked-by: Ian Kent Signed-off-by: Al Viro