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path: root/fs/locks.c
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2015-02-02fs: add FL_LAYOUT lease typeChristoph Hellwig
This (ab-)uses the file locking code to allow filesystems to recall outstanding pNFS layouts on a file. This new lease type is similar but not quite the same as FL_DELEG. A FL_LAYOUT lease can always be granted, an a per-filesystem lock (XFS iolock for the initial implementation) ensures not FL_LAYOUT leases granted when we would need to recall them. Also included are changes that allow multiple outstanding read leases of different types on the same file as long as they have a differnt owner. This wasn't a problem until now as nfsd never set FL_LEASE leases, and no one else used FL_DELEG leases, but given that nfsd will also issues FL_LAYOUT leases we will have to handle it now. Signed-off-by: Christoph Hellwig <hch@lst.de>
2015-02-02fs: track fl_owner for leasesChristoph Hellwig
Just like for other lock types we should allow different owners to have a read lease on a file. Currently this can't happen, but with the addition of pNFS layout leases we'll need this feature. Signed-off-by: Christoph Hellwig <hch@lst.de>
2015-01-21locks: update comments that refer to inode->i_flockJeff Layton
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2015-01-16locks: consolidate NULL i_flctx checks in locks_remove_fileJeff Layton
We have each of the locks_remove_* variants doing this individually. Have the caller do it instead, and have locks_remove_flock and locks_remove_lease just assume that it's a valid pointer. Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2015-01-16locks: keep a count of locks on the flctx listsJeff Layton
This makes things a bit more efficient in the cifs and ceph lock pushing code. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: clean up the lm_change prototypeJeff Layton
Now that we use standard list_heads for tracking leases, we can have lm_change take a pointer to the lease to be modified instead of a double pointer. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: add a dedicated spinlock to protect i_flctx listsJeff Layton
We can now add a dedicated spinlock without expanding struct inode. Change to using that to protect the various i_flctx lists. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: convert lease handling to file_lock_contextJeff Layton
Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: convert posix locks to file_lock_contextJeff Layton
Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: move flock locks to file_lock_contextJeff Layton
Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: add a new struct file_locking_context pointer to struct inodeJeff Layton
The current scheme of using the i_flock list is really difficult to manage. There is also a legitimate desire for a per-inode spinlock to manage these lists that isn't the i_lock. Start conversion to a new scheme to eventually replace the old i_flock list with a new "file_lock_context" object. We start by adding a new i_flctx to struct inode. For now, it lives in parallel with i_flock list, but will eventually replace it. The idea is to allocate a structure to sit in that pointer and act as a locus for all things file locking. We allocate a file_lock_context for an inode when the first lock is added to it, and it's only freed when the inode is freed. We use the i_lock to protect the assignment, but afterward it should mostly be accessed locklessly. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-16locks: have locks_release_file use flock_lock_file to release generic flock ↵Jeff Layton
locks ...instead of open-coding it and removing flock locks directly. This helps consolidate the flock lock removal logic into a single spot. Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2015-01-16locks: add new struct list_head to struct file_lockJeff Layton
...that we can use to queue file_locks to per-ctx list_heads. Go ahead and convert locks_delete_lock and locks_dispose_list to use it instead of the fl_block list. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Acked-by: Christoph Hellwig <hch@lst.de>
2015-01-13locks: fix NULL-deref in generic_delete_leaseNeilBrown
commit 0efaa7e82f02fe69c05ad28e905f31fc86e6f08e locks: generic_delete_lease doesn't need a file_lock at all moves the call to fl->fl_lmops->lm_change() to a place in the code where fl might be a non-lease lock. When that happens, fl_lmops is NULL and an Oops ensures. So add an extra test to restore correct functioning. Reported-by: Linda Walsh <suse@tlinx.org> Link: https://bugzilla.suse.com/show_bug.cgi?id=912569 Cc: stable@vger.kernel.org (v3.18) Fixes: 0efaa7e82f02fe69c05ad28e905f31fc86e6f08e Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-10-07locks: flock_make_lock should return a struct file_lock (or PTR_ERR)Jeff Layton
Eliminate the need for a return pointer. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: set fl_owner for leases to filp instead of current->filesJeff Layton
Like flock locks, leases are owned by the file description. Now that the i_have_this_lease check in __break_lease is gone, we don't actually use the fl_owner for leases for anything. So, it's now safe to set this more appropriately to the same value as the fl_file. While we're at it, fix up the comments over the fl_owner_t definition since they're rather out of date. Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-10-07locks: give lm_break a return valueJeff Layton
Christoph suggests: "Add a return value to lm_break so that the lock manager can tell the core code "you can delete this lease right now". That gets rid of the games with the timeout which require all kinds of race avoidance code in the users." Do that here and have the nfsd lease break routine use it when it detects that there was a race between setting up the lease and it being broken. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: __break_lease cleanup in preparation of allowing direct removal of leasesJeff Layton
Eliminate an unneeded "flock" variable. We can use "fl" as a loop cursor everywhere. Add a any_leases_conflict helper function as well to consolidate a bit of code. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: remove i_have_this_lease check from __break_leaseJeff Layton
I think that the intent of this code was to ensure that a process won't deadlock if it has one fd open with a lease on it and then breaks that lease by opening another fd. In that case it'll treat the __break_lease call as if it were non-blocking. This seems wrong -- the process could (for instance) be multithreaded and managing different fds via different threads. I also don't see any mention of this limitation in the (somewhat sketchy) documentation. Remove the check and the non-blocking behavior when i_have_this_lease is true. Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-10-07locks: move freeing of leases outside of i_lockJeff Layton
There was only one place where we still could free a file_lock while holding the i_lock -- lease_modify. Add a new list_head argument to the lm_change operation, pass in a private list when calling it, and fix those callers to dispose of the list once the lock has been dropped. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: move i_lock acquisition into generic_*_lease handlersJeff Layton
Now that we have a saner internal API for managing leases, we no longer need to mandate that the inode->i_lock be held over most of the lease code. Push it down into generic_add_lease and generic_delete_lease. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: define a lm_setup handler for leasesJeff Layton
...and move the fasync setup into it for fcntl lease calls. At the same time, change the semantics of how the file_lock double-pointer is handled. Up until now, on a successful lease return you got a pointer to the lock on the list. This is bad, since that pointer can no longer be relied on as valid once the inode->i_lock has been released. Change the code to instead just zero out the pointer if the lease we passed in ended up being used. Then the callers can just check to see if it's NULL after the call and free it if it isn't. The priv argument has the same semantics. The lm_setup function can zero the pointer out to signal to the caller that it should not be freed after the function returns. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: plumb a "priv" pointer into the setlease routinesJeff Layton
In later patches, we're going to add a new lock_manager_operation to finish setting up the lease while still holding the i_lock. To do this, we'll need to pass a little bit of info in the fcntl setlease case (primarily an fasync structure). Plumb the extra pointer into there in advance of that. We declare this pointer as a void ** to make it clear that this is private info, and that the caller isn't required to set this unless the lm_setup specifically requires it. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: clean up vfs_setlease kerneldoc commentsJeff Layton
Some of the latter paragraphs seem ambiguous and just plain wrong. In particular the break_lease comment makes no sense. We call break_lease (and break_deleg) from all sorts of vfs-layer functions, so there is clearly such a method. Also get rid of some of the other comments about what's needed for a full implementation. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: generic_delete_lease doesn't need a file_lock at allJeff Layton
Ensure that it's OK to pass in a NULL file_lock double pointer on a F_UNLCK request and convert the vfs_setlease F_UNLCK callers to do just that. Finally, turn the BUG_ON in generic_setlease into a WARN_ON_ONCE with an error return. That's a problem we can handle without crashing the box if it occurs. Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-10-07locks: close potential race in lease_get_mtimeJeff Layton
lease_get_mtime is called without the i_lock held, so there's no guarantee about the stability of the list. Between the time when we assign "flock" and then dereference it to check whether it's a lease and for write, the lease could be freed. Ensure that that doesn't occur by taking the i_lock before trying to check the lease. Cc: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-09-09security: make security_file_set_fowner, f_setown and __f_setown void returnJeff Layton
security_file_set_fowner always returns 0, so make it f_setown and __f_setown void return functions and fix up the error handling in the callers. Cc: linux-security-module@vger.kernel.org Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-09-09locks: remove lock_may_read and lock_may_writeJeff Layton
There are no callers of these functions. Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-09-09locks: Copy fl_lmops information for conflock in locks_copy_conflock()Kinglong Mee
Commit d5b9026a67 ([PATCH] knfsd: locks: flag NFSv4-owned locks) using fl_lmops field in file_lock for checking nfsd4 lockowner. But, commit 1a747ee0cc (locks: don't call ->copy_lock methods on return of conflicting locks) causes the fl_lmops of conflock always be NULL. Also, commit 0996905f93 (lockd: posix_test_lock() should not call locks_copy_lock()) caused the fl_lmops of conflock always be NULL too. Make sure copy the private information by fl_copy_lock() in struct file_lock_operations, merge __locks_copy_lock() to fl_copy_lock(). Jeff advice, "Set fl_lmops on conflocks, but don't set fl_ops. fl_ops are superfluous, since they are callbacks into the filesystem. There should be no need to bother the filesystem at all with info in a conflock. But, lock _ownership_ matters for conflocks and that's indicated by the fl_lmops. So you really do want to copy the fl_lmops for conflocks I think." v5: add missing calling of locks_release_private() in nlmsvc_testlock() v4: only copy fl_lmops for conflock, don't copy fl_ops Signed-off-by: Kinglong Mee <kinglongmee@gmail.com> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-09-09locks: New ops in lock_manager_operations for get/put ownerKinglong Mee
NFSD or other lockmanager may increase the owner's reference, so adds two new options for copying and releasing owner. v5: change order from 2/6 to 3/6 v4: rename lm_copy_owner/lm_release_owner to lm_get_owner/lm_put_owner Reviewed-by: Jeff Layton <jlayton@primarydata.com> Signed-off-by: Kinglong Mee <kinglongmee@gmail.com> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-09-09locks: Rename __locks_copy_lock() to locks_copy_conflock()Kinglong Mee
Jeff advice, " Right now __locks_copy_lock is only used to copy conflocks. It would be good to rename that to something more distinct (i.e.locks_copy_conflock), to make it clear that we're generating a conflock there." v5: change order from 3/6 to 2/6 v4: new patch only renaming function name Signed-off-by: Kinglong Mee <kinglongmee@gmail.com> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-09-09locks: pass correct "before" pointer to locks_unlink_lock in generic_add_leaseJeff Layton
The argument to locks_unlink_lock can't be just any pointer to a pointer. It must be a pointer to the fl_next field in the previous lock in the list. Cc: <stable@vger.kernel.org> # v3.15+ Signed-off-by: Jeff Layton <jlayton@primarydata.com> Reviewed-by: Christoph Hellwig <hch@lst.de>
2014-08-14locks: move locks_free_lock calls in do_fcntl_add_lease outside spinlockJeff Layton
There's no need to call locks_free_lock here while still holding the i_lock. Defer that until the lock has been dropped. Acked-by: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-08-14locks: defer freeing locks in locks_delete_lock until after i_lock has been ↵Jeff Layton
dropped In commit 72f98e72551fa (locks: turn lock_flocks into a spinlock), we moved from using the BKL to a global spinlock. With this change, we lost the ability to block in the fl_release_private operation. This is problematic for NFS (and probably some other filesystems as well). Add a new list_head argument to locks_delete_lock. If that argument is non-NULL, then queue any locks that we want to free to the list instead of freeing them. Then, add a new locks_dispose_list function that will walk such a list and call locks_free_lock on them after the i_lock has been dropped. Finally, change all of the callers of locks_delete_lock to pass in a list_head, except for lease_modify. That function can be called long after the i_lock has been acquired. Deferring the freeing of a lease after unlocking it in that function is non-trivial until we overhaul some of the spinlocking in the lease code. Currently though, no filesystem that sets fl_release_private supports leases, so this is not currently a problem. We'll eventually want to make the same change in the lease code, but it needs a lot more work before we can reasonably do so. Acked-by: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-08-14locks: don't reuse file_lock in __posix_lock_fileJeff Layton
Currently in the case where a new file lock completely replaces the old one, we end up overwriting the existing lock with the new info. This means that we have to call fl_release_private inside i_lock. Change the code to instead copy the info to new_fl, insert that lock into the correct spot and then delete the old lock. In a later patch, we'll defer the freeing of the old lock until after the i_lock has been dropped. Acked-by: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-08-11locks: don't call locks_release_private from locks_copy_lockJeff Layton
All callers of locks_copy_lock pass in a brand new file_lock struct, so there's no need to call locks_release_private on it. Replace that with a warning that fires in the event that we receive a target lock that doesn't look like it's properly initialized. Acked-by: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-08-11locks: show delegations as "DELEG" in /proc/locksJeff Layton
Now that they are a distinct lease type, show them as such. Cc: J. Bruce Fields <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-07-13locks: purge fl_owner_t from fs/locks.cChristoph Hellwig
Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-06-10locks: set fl_owner for leases back to current->filesJeff Layton
This fixes a regression due to commit 130d1f956ab3 (locks: ensure that fl_owner is always initialized properly in flock and lease codepaths). I had mistakenly thought that the fl_owner wasn't used in the lease code, but I missed the place in __break_lease that does use it. The i_have_this_lease check in generic_add_lease uses it. While I'm not sure that check is terribly helpful [1], reset it back to using current->files in order to ensure that there's no behavior change here. [1]: leases are owned by the file description. It's possible that this is a threaded program, and the lease breaker and the task that would handle the signal are different, even if they have the same file table. So, there is the potential for false positives with this check. Fixes: 130d1f956ab3 (locks: ensure that fl_owner is always initialized properly in flock and lease codepaths) Signed-off-by: Jeff Layton <jlayton@primarydata.com>
2014-06-02locks: add some tracepoints in the lease handling codeJeff Layton
v2: add a __break_lease tracepoint for non-blocking case Recently, I needed these to help track down a softlockup when recalling a delegation, but they might be helpful in other situations as well. Cc: "J. Bruce Fields" <bfields@fieldses.org> Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
2014-06-02fs/locks.c: replace seq_printf by seq_putsFabian Frederick
Replace seq_printf where possible Cc: Jeff Layton <jlayton@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Fabian Frederick <fabf@skynet.be> Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
2014-06-02locks: ensure that fl_owner is always initialized properly in flock and ↵Jeff Layton
lease codepaths Currently, the fl_owner isn't set for flock locks. Some filesystems use byte-range locks to simulate flock locks and there is a common idiom in those that does: fl->fl_owner = (fl_owner_t)filp; fl->fl_start = 0; fl->fl_end = OFFSET_MAX; Since flock locks are generally "owned" by the open file description, move this into the common flock lock setup code. The fl_start and fl_end fields are already set appropriately, so remove the unneeded setting of that in flock ops in those filesystems as well. Finally, the lease code also sets the fl_owner as if they were owned by the process and not the open file description. This is incorrect as leases have the same ownership semantics as flock locks. Set them the same way. The lease code doesn't actually use the fl_owner value for anything, so this is more for consistency's sake than a bugfix. Reported-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Jeff Layton <jlayton@poochiereds.net> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> (Staging portion) Acked-by: J. Bruce Fields <bfields@fieldses.org>
2014-05-09locks: only validate the lock vs. f_mode in F_SETLK codepathsJeff Layton
v2: replace missing break in switch statement (as pointed out by Dave Jones) commit bce7560d4946 (locks: consolidate checks for compatible filp->f_mode values in setlk handlers) introduced a regression in the F_GETLK handler. flock64_to_posix_lock is a shared codepath between F_GETLK and F_SETLK, but the f_mode checks should only be applicable to the F_SETLK codepaths according to POSIX. Instead of just reverting the patch, add a new function to do this checking and have the F_SETLK handlers call it. Cc: Dave Jones <davej@redhat.com> Reported-and-Tested-by: Reuben Farrelly <reuben@reub.net> Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
2014-04-23locks: rename FL_FILE_PVT and IS_FILE_PVT to use "*_OFDLCK" insteadJeff Layton
File-private locks have been re-christened as "open file description" locks. Finish the symbol name cleanup in the internal implementation. Signed-off-by: Jeff Layton <jlayton@redhat.com>
2014-04-22locks: rename file-private locks to "open file description locks"Jeff Layton
File-private locks have been merged into Linux for v3.15, and *now* people are commenting that the name and macro definitions for the new file-private locks suck. ...and I can't even disagree. The names and command macros do suck. We're going to have to live with these for a long time, so it's important that we be happy with the names before we're stuck with them. The consensus on the lists so far is that they should be rechristened as "open file description locks". The name isn't a big deal for the kernel, but the command macros are not visually distinct enough from the traditional POSIX lock macros. The glibc and documentation folks are recommending that we change them to look like F_OFD_{GETLK|SETLK|SETLKW}. That lessens the chance that a programmer will typo one of the commands wrong, and also makes it easier to spot this difference when reading code. This patch makes the following changes that I think are necessary before v3.15 ships: 1) rename the command macros to their new names. These end up in the uapi headers and so are part of the external-facing API. It turns out that glibc doesn't actually use the fcntl.h uapi header, but it's hard to be sure that something else won't. Changing it now is safest. 2) make the the /proc/locks output display these as type "OFDLCK" Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Christoph Hellwig <hch@infradead.org> Cc: Carlos O'Donell <carlos@redhat.com> Cc: Stefan Metzmacher <metze@samba.org> Cc: Andy Lutomirski <luto@amacapital.net> Cc: Frank Filz <ffilzlnx@mindspring.com> Cc: Theodore Ts'o <tytso@mit.edu> Signed-off-by: Jeff Layton <jlayton@redhat.com>
2014-04-15locks: allow __break_lease to sleep even when break_time is 0Jeff Layton
A fl->fl_break_time of 0 has a special meaning to the lease break code that basically means "never break the lease". knfsd uses this to ensure that leases don't disappear out from under it. Unfortunately, the code in __break_lease can end up passing this value to wait_event_interruptible as a timeout, which prevents it from going to sleep at all. This makes __break_lease to spin in a tight loop and causes soft lockups. Fix this by ensuring that we pass a minimum value of 1 as a timeout instead. Cc: <stable@vger.kernel.org> Cc: J. Bruce Fields <bfields@fieldses.org> Reported-by: Terry Barnaby <terry1@beam.ltd.uk> Signed-off-by: Jeff Layton <jlayton@redhat.com>
2014-03-31locks: make locks_mandatory_area check for file-private locksJeff Layton
Allow locks_mandatory_area() to handle file-private locks correctly. If there is a file-private lock set on an open file and we're doing I/O via the same, then that should not cause anything to block. Handle this by first doing a non-blocking FL_ACCESS check for a file-private lock, and then fall back to checking for a classic POSIX lock (and possibly blocking). Note that this approach is subject to the same races that have always plagued mandatory locking on Linux. Reported-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Jeff Layton <jlayton@redhat.com>
2014-03-31locks: fix locks_mandatory_locked to respect file-private locksJeff Layton
As Trond pointed out, you can currently deadlock yourself by setting a file-private lock on a file that requires mandatory locking and then trying to do I/O on it. Avoid this problem by plumbing some knowledge of file-private locks into the mandatory locking code. In order to do this, we must pass down information about the struct file that's being used to locks_verify_locked. Reported-by: Trond Myklebust <trond.myklebust@primarydata.com> Signed-off-by: Jeff Layton <jlayton@redhat.com> Acked-by: J. Bruce Fields <bfields@redhat.com>
2014-03-31locks: require that flock->l_pid be set to 0 for file-private locksJeff Layton
Neil Brown suggested potentially overloading the l_pid value as a "lock context" field for file-private locks. While I don't think we will probably want to do that here, it's probably a good idea to ensure that in the future we could extend this API without breaking existing callers. Typically the l_pid value is ignored for incoming struct flock arguments, serving mainly as a place to return the pid of the owner if there is a conflicting lock. For file-private locks, require that it currently be set to 0 and return EINVAL if it isn't. If we eventually want to make a non-zero l_pid mean something, then this will help ensure that we don't break legacy programs that are using file-private locks. Cc: Neil Brown <neilb@suse.de> Signed-off-by: Jeff Layton <jlayton@redhat.com>
2014-03-31locks: add new fcntl cmd values for handling file private locksJeff Layton
Due to some unfortunate history, POSIX locks have very strange and unhelpful semantics. The thing that usually catches people by surprise is that they are dropped whenever the process closes any file descriptor associated with the inode. This is extremely problematic for people developing file servers that need to implement byte-range locks. Developers often need a "lock management" facility to ensure that file descriptors are not closed until all of the locks associated with the inode are finished. Additionally, "classic" POSIX locks are owned by the process. Locks taken between threads within the same process won't conflict with one another, which renders them useless for synchronization between threads. This patchset adds a new type of lock that attempts to address these issues. These locks conflict with classic POSIX read/write locks, but have semantics that are more like BSD locks with respect to inheritance and behavior on close. This is implemented primarily by changing how fl_owner field is set for these locks. Instead of having them owned by the files_struct of the process, they are instead owned by the filp on which they were acquired. Thus, they are inherited across fork() and are only released when the last reference to a filp is put. These new semantics prevent them from being merged with classic POSIX locks, even if they are acquired by the same process. These locks will also conflict with classic POSIX locks even if they are acquired by the same process or on the same file descriptor. The new locks are managed using a new set of cmd values to the fcntl() syscall. The initial implementation of this converts these values to "classic" cmd values at a fairly high level, and the details are not exposed to the underlying filesystem. We may eventually want to push this handing out to the lower filesystem code but for now I don't see any need for it. Also, note that with this implementation the new cmd values are only available via fcntl64() on 32-bit arches. There's little need to add support for legacy apps on a new interface like this. Signed-off-by: Jeff Layton <jlayton@redhat.com>