What is the behavior with "nobrl" mount option? and what is the behavior when running with the POSIX extensions enabled (e.g. to current Samba or ksmbd adding "posix" to the mount options) On Thu, May 23, 2024 at 11:08 AM Kevin Ottens <kevin.ottens@xxxxxxxxxx> wrote: > > Hello, > > I've been hunting down a bug exhibited by Libreoffice regarding POSIX file > locks in conjunction with CIFS mounts. In short: just before saving, it > reopens a file on which it already holds a file lock (via another file > descriptor in the same process) in order to read from it to create a backup > copy... but the read call fails. > > I've been in discussion with Andrew Bartlett for a little while regarding this > issue and, after exploring several venues, he advised me to send an email to > this list in order to get more opinions about it. > > The latest discovery we did was that the cache option on the mountpoint seems > to impact the behavior of the POSIX file locks. I made a minimal test > application (attached to this email) which basically does the following: > * open a file for read/write > * set a POSIX write lock on the whole file > * open the file a second time and try to read from it > * open the file a third time and try to write to it > > It assumes there is already some text in the file. Also, as it goes it outputs > information about the calls. > > The output I get is the following with cache=strict on the mount: > --- > Testing with /mnt/foo > Got new file descriptor 3 > Lock set: 1 > Second file descriptor 4 > Read from second fd: x count: -1 > Third file descriptor 5 > Wrote to third fd: -1 > --- > > If I'm using cache=none: > --- > Testing with /mnt/foo > Got new file descriptor 3 > Lock set: 1 > Second file descriptor 4 > Read from second fd: b count: 1 > Third file descriptor 5 > Wrote to third fd: 1 > --- > > That's the surprising behavior which prompted the email on this list. Is it > somehow intended that the cache option would impact the semantic of the file > locks? At least it caught me by surprise and I wouldn't expect such a > difference in behavior. > > Now, since the POSIX locks are process wide, I would have expected to have the > output I'm getting for the "cache=none" case to be also the one I'm getting > for the "cache=strict" case. > > I'm looking forward to feedback on this one. I really wonder if we missed > something obvious or if there is some kind of bug in the cifs driver. > > Regards. > -- > Kévin Ottens > kevin.ottens@xxxxxxxxxx > +33 7 57 08 95 13 -- Thanks, Steve
