On 7/29/20 2:41 PM, Eric Sandeen wrote:
On 7/29/20 11:32 AM, Josef Bacik wrote:
Hello,
Eric reported a problem to me where we were clearing SB_I_VERSION on remount of a btrfs file system. After digging through I discovered it's because we expect the proper flags that we want to be passed in via the mount() syscall, and because we didn't have "iversion" in our show_options entry the mount binary (form util-linux) wasn't setting MS_I_VERSION for the remount, and thus the VFS was clearing SB_I_VERSION from our s_flags.
No big deal, I'll fix show_mount. Except Eric then noticed that mount -o noiversion didn't do anything, we still get iversion set. That's because btrfs just defaults to having SB_I_VERSION set. Furthermore -o noiversion doesn't get sent into mount, it's handled by the mount binary itself, and it does this by not having MS_I_VERSION set in the mount flags.
This was beaten^Wdiscussed to death in an earlier thread,
[PATCH] fs: i_version mntopt gets visible through /proc/mounts
https://lore.kernel.org/linux-fsdevel/20200616202123.12656-1-msys.mizuma@xxxxxxxxx/
tl;dr: hch doesn't think [no]iversion should be exposed as an option /at all/
so exposing it in /proc/mounts in show_mnt_opts for mount(8)'s benefit was
nacked.
This happens as well for -o relatime, it's the default and so if you do mount -o norelatime it won't do anything, you still get relatime behavior.
I think that's a different issue.
The only time this changes is if you do mount -o remount,norelatime.
Hm, not on xfs:
# mount -o loop,norelatime xfsfile mnt
# grep loop /proc/mounts
/dev/loop0 /tmp/mnt xfs rw,seclabel,relatime,attr2,inode64,logbufs=8,logbsize=32k,noquota 0 0
# mount -o remount,norelatime mnt
# grep loop /proc/mounts
/dev/loop0 /tmp/mnt xfs rw,seclabel,relatime,attr2,inode64,logbufs=8,logbsize=32k,noquota 0 0
Oops you're right, I'm blind. Same happens for btrfs, so using -o norelatime
simply does nothing because it's considered a kernel wide default.
Are there other oddities besides iversion and relatime?
It doesn't look like it, I checked a few others of the MS_INVERT variety, these
appear to be the only ones. I really don't want to have this discussion again
in the future tho when we introduce MS_SOME_NEW_AWESOME. Thanks,
Josef
