On 25/08/14 12:37PM, Miklos Szeredi wrote: > On Sat, 12 Jul 2025 at 07:54, Darrick J. Wong <djwong@xxxxxxxxxx> wrote: > > > > On Fri, Jul 11, 2025 at 10:28:20AM -0500, John Groves wrote: > > > > famfs_fuse: Basic famfs mount opt: -o shadow=<shadowpath> > > > > > > The shadow path is a (usually tmpfs) file system area used by the famfs > > > user space to commuicate with the famfs fuse server. There is a minor > > > dilemma that the user space tools must be able to resolve from a mount > > > point path to a shadow path. The shadow path is exposed via /proc/mounts, > > > but otherwise not used by the kernel. User space gets the shadow path > > > from /proc/mounts... > > Don't know if we want to go that way. Is there no other way? > > But if we do, at least do it in a generic way. I.e. fuse server can > tell the kernel to display options A, B and C in /proc/mounts. > > Thanks, > Miklos So far I haven't come up with an alternative, other than bad ones. Could parse the shadow path from the fuse server with the correct mount point from 'ps -ef', but there are cases where a fuse server is killed and the kernel still thinks it's mounted (and we still might need to find the shadow path). Could write the shadow path to a systemd log and parse it from there, but that would break if the log wasn't enabled, and would disappear if the log was rotated during a long-running mount - and this resolution must happen every time the famfs cli does most anything (cp, creat, fsck, etc.). Could write it to a "secret file" somewhere, but that's kinda brittle. Shadow paths are almost always tmpdir paths that are generated at mount time, so there really isn't a good way to guess them, and it doesn't seem viable to require them to be in (e.g.) /tmp in all cases. Here is what it currently looks like on a running system: $ grep famfs /proc/mounts /dev/dax0.0 /mnt/famfs fuse rw,nosuid,nodev,relatime,user_id=0,group_id=0,shadow=/tmp/famfs_shadow_5m0dnH 0 0 $ ps -ef | grep /mnt/famfs | grep -v grep root 12775 1 0 07:04 ? 00:00:00 /dev/dax0.0 -o daxdev=/dev/dax0.0,shadow=/tmp/famfs_shadow_5m0dnH,fsname=/dev/dax0.0,timeout=31536000.000000 /mnt/famfs Having a generic approach rather than a '-o' option would be fine with me. Also happy to entertain other ideas... Thanks, John
