Messages in this thread | | | Date | Mon, 10 Apr 2006 23:13:30 -0400 | From | Amy Griffis <> | Subject | Re: [RFC][PATCH] inotify kernel api |
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John McCutchan wrote: [Mon Apr 10 2006, 02:36:28PM EDT] > On Thu, 2006-04-06 at 13:06 -0400, Amy Griffis wrote: > > The following patch against 2.6.17-rc1-mm1 introduces a kernel API for inotify. > > > > Event processing is unchanged except for the indirection added for the > > callback. In inotify_user.c, an additional per-device mutex is held > > while adding watches to prevent adding the same watch twice. The > > design retains the original assumption that there will be more watches > > per inotify_handle than watches on any given inode, and performs the > > search for existing watches accordingly. > > > > Why do we need the 'up_mutex' mutex? Was this a bug in the old code?
The up_mutex is needed to ensure that a watch that does not exist when calling inotify_find_update_watch() still does not exist when calling inotify_add_watch(). It seemed to me that the find/update and add functions needed to be separated for the kernel api.
Unfortunately we can't use dev->ev_mutex here as it's taken during the callback.
> > This patch makes the inotify_watch public so it can be embedded in callers' own > > watch structures, which avoids the use of a void ptr to caller data. > > Even though inotify_watch is public, callers must use the established > > interfaces to access inotify_watch contents. Was this the best > > choice? > > > > I suppose this is an alright change. As long as it is understood that > there is no guarantee about the layout of the inotify_watch structure. A > comment in inotify.h should do.
Done.
* Callers must use the established inotify interfaces to access inotify_watch * contents. The content of this structure is private to the inotify * implementation.
> > I think the locking may be less than ideal, as the > > inode->inotify_mutex must be held to traverse the inode's watchlist, > > and thus must be held during the callback. The result is that the > > caller can't hold any locks taken during callback processing while > > calling any of the published inotify interfaces, making > > synchronization a little more difficult. > > > > Well, I think it's up for the kernel consumers to decide whether or not > this is acceptable. It's probably a good idea to come up with some use > cases for the kernel API and see if this _is_ a problem. Since the > callbacks will be run inside the VFS ops, they need to be small and > fast, so they probably should just be putting the event on a list and > handling it later. > > Looking over the patch, nothing jumps out at me as being wrong. But some > stress testing would convince me faster than my eyes can.
I'll follow up with some stress test results.
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