On Wednesday 14 November 2012 14:13:41 Pavel Emelyanov wrote: > On 11/14/2012 02:08 PM, Tvrtko Ursulin wrote: > > On Wednesday 14 November 2012 13:58:12 Cyrill Gorcunov wrote: > >> On Wed, Nov 14, 2012 at 09:50:55AM +0000, Tvrtko Ursulin wrote: > >>>>> You could not use a pointer and then allocate your buffers on the > >>>>> check > >>>>> point operation, freeing on restore? > >>>> > >>>> The problem is not allocating the memory itself but rather the time > >>>> when > >>>> the information needed (ie the dentry) is available. The only moment > >>>> when we can use dentry of the target file/directory is at > >>>> inotify_new_watch, that's why i need to compose fhandle that early. At > >>>> any later point we simply have no dentry to use. > >>> > >>> But you do not fundamentally need the dentry to restore a watch, right? > >> > >> dentry only needed to encode the file handle. > >> > >>> Couldn't you restore, creating a new restore path if needed, using the > >>> inode which is pinned anyway while the watch exists? > >> > >> plain inode is not enough as far as i can tell, iow i don't see the way > >> to restore path from inode solely. or there something i miss? > > > > I don't know, as I said I was not following this at all until now. Just > > throwing in ideas. > > > > I thought, since inotify does not use the path or dentry outside the > > system > > call at all, perhaps you need a different entry point allowing you to > > restore the watch using the inode or something. Assuming life time of > > objects and stuff in C&R world would allow you that. Since you don't need > > the full path, just something 64 bytes long, I assumed that could be the > > case. > > Well, the kernel already has all the API we need but one -- it shows us > _nothing_ about the inode being watched. And we'd appreciate any > information about it. Even the ino:dev pair would work. We propose to show > the handle because we believe, that such API is better that ino:dev. You > can get the handle, call the open_by_handle_at right at once and get much > much more information about the inode with any other API (e.g. calling > fstat() will give you the ino:dev pair). Having just ino:dev pair at hands > is not that flexible. How much space does a typical file system need to encode a handle? Am I right that for must it is just a few bytes? (I just glanced at the code so I might be wrong.) In which case, could the handle buffer be allocated dynamically depending on the underlying filesystem? Perhaps adding a facility to query a filesystem about its maximum handle buffer needs? Do you think the saving would justify this extra work? Regards, Tvrtko -- 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
