File Name Too Long?

Priyadarshan
Fri, 30 Sep 2016 14:39:06 -0000

On Fri, 30 Sep 2016, at 14:34, Dean E. Weimer wrote:
> On 2016-09-29 9:32 am, Dean E. Weimer wrote:
> > I discovered, unfortunately by deleting a jail by accident, that my
> > backup process isn't working. At least it was only the operating
> > system part of the jail, I still have all the data so I just need to
> > reinstall the operating system. While the ports are in the process of
> > building I started to investigate the cause, because the backup logs
> > report everything was fine.
> >
> > I have a custom pre-backup script I wrote that takes snapshots of my
> > ZFS datasets, and then mounts those under /mnt/backup with nullfs
> > mount points to the .zfs/snapshot/.. directories then I back them up
> > rather than the live file system, allowing me to stop some services
> > that don't restore from a running state correctly and then restart
> > after the snapshot so downtime is only a couple of minutes instead of
> > full length of backups.
> >
> > It appeared to be running perfectly, without errors, but apparently
> > the script isn't reporting some nullfs mount failures, so why are
the
> > failing, turns out it thinks the file name is too long? but looking at
> > the mount(2) man page it states this:
> >
> > [ENAMETOOLONG]     A component of a pathname exceeded 255 characters,
> > or
> >                         the entire length of a path name exceeded 1023
> >                         characters.
> >
> > I can see that at some point under this, I may reach that 1023 limit,
> > but what of the total 71 characters in this path has a problem?
> >
> > /jails/unifi/ROOT/.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
> >
> > root at freebsd:/jails/unifi/ROOT/.zfs/snapshot # ls
> > ls: 11.0-RELEASE-r306379-2016.09.28--bsnap: File name too long
> >
> > I thought, maybe its a ZFS specific error, and ran across this:
> > http://lists.freebsd.org/pipermail/freebsd-fs/2010-March/007964.html
> >
> > [..snip..]
> > From looking at the code, I think you hitting this limit:
> >
> > 	/*
> > 	 * Be ultra-paranoid about making sure the type and fspath
> > 	 * variables will fit in our mp buffers, including the
> > 	 * terminating NUL.
> > 	 */
> > 	if (strlen(fstype) >= MFSNAMELEN || strlen(fspath) >= MNAMELEN)
> > 		return (ENAMETOOLONG);
> >
> > in vfs_domount() or vfs_donmount().
> >
> > This is FreeBSD limit caused by statfs structure:
> >
> > /*
> >  * filesystem statistics
> >  */
> > [...]
> > #define MNAMELEN        88              /* size of on/from name bufs
*/
> > [...]
> > struct statfs {
> > [...]
> > 	char	f_mntfromname[MNAMELEN];/* mounted filesystem */
> > 	char	f_mntonname[MNAMELEN];	/* directory on which mounted */
> > };
> >
> > When you list .zfs/snapshot/ directory (especially with -l option) ZFS
> > mounts snapshots on lookup and this is this mount that fails.
> > [..snip..]
> >
> > I can seemingly due anything else with the snapshot, clone, send,
> > receive its just that I am unable to access the files on it through
> > .zfs/snapshot/..
> >
> > I am trying to find what the limit is here from this, because this one
> > here works.
> >
> >
/jails/webmail/usr-local-subversion/.zfs/snapshot/usr-local-subversion--bsnap
> >
> > its longer in total length than most of the ones that are failing.
> >
> > /jails/unifi/ROOT/.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
> >
> > So it appears that its in the name, and not the mount point.
> >
> > this one works as well, which is my ZFS boot environment on the main
> > system
> > zraid/ROOT/11.0-RELEASE-r306379-2016.09.28
> > snapshot is /.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
> >
> > So its not just the last component of the zfs dataset name, which is
> > in this case the same.
> >
> > I am trying to wrap my head around this and find where the limit is so
> > I can adjust my naming conventions used and actually get backups of
> > all of my data. Turns out all of my jail operating system paths
aren't
> > being backed up, fortunately at least all of the data file systems for
> > the jails are.
>
> I found a solution, I was naming the snapshots with the dataset name,
> which I think was causing the issue.
>
> The following didn't seem to long to be an issue
> /jails/unifi/ROOT/.zfs/snapshot/11.0-RELEASE-r306379-2016.09.28--bsnap
>
> But apparently the snapshot name was
> zraid/jails/unifi/11.0-RELEASE-r306379-2016.09.28 at
11.0-RELEASE-r306379-2016.09.28--bsnap
>
> Still not sure how it adds up to too long, both full paths together
> aren't over 255, at 160, but apparently something else is added in
> there. I was able to easily modify my backup script to not include the
> last part of the dataset in the snapshot name and simply use -bsnap-, as
> the name. it appears to avoid all the issues, and my backups from last
> night include all the files.
>
> /jails/unifi/ROOT/.zfs/snapshot/-bsnap-
> zraid/jails/unifi/11.0-RELEASE-r306379-2016.09.28 at -bsnap-
>
> The total path now only adds up to 98, I haven't done any testing yet
to
> find out where the limit is hit, The longest combination of these I had
> last night would have added up to 135, and that worked
>
> --
> Thanks,
>     Dean E. Weimer
>     http://www.dweimer.net/


This may be related:

http://iocage.readthedocs.io/en/latest/known-issues.html#character-mount-path-limitation

Priyadarshan