On 04.03.21 17:39, Dr. David Alan Gilbert wrote:
* Max Reitz ([email protected]) wrote:
On 03.03.21 19:20, Vivek Goyal wrote:
Hi Max,
Hi Vivek,
I was playing with "announce_submounts". I have a read-only bind mounted
mount point in shared directory. Inside guest, when I step into that
directory, I see that a mount point got created but its "rw" and not "ro".
Is that intentional.
No, that isn’t intentional. I just didn’t think of sharing such information
with the guest.
Can we send property of mount also to guest when
notifying guest about mount point.
I suppose we can send it (by adding a new flag alongside
FUSE_ATTR_SUBMOUNT), and we can make the mount ro by setting the SB_RDONLY
flag in fuse_dentry_automount().
If we implemented this for RDONLY, are there other flags that we might want
to consider as well? (e.g. nodev etc.)
OTOH, I just tested NFS, and it doesn’t pass through the RO flag:
[...]
/tmp/xfs.img on ~/tmp/test-nfs/mount type xfs (ro,...)
[...]
127.0.0.1:~/tmp/test-nfs on /mnt/tmp type nfs4 (rw,...)
127.0.0.1:~/tmp/test-nfs/mount on /mnt/tmp/mount type nfs4 (rw,...)
So is it really important or more a matter of style?
So what happens if you try and write a file in /mnt/tmp/mount ?
Well, the EROFS gets passed through from host to client:
$ LANG=C sudo touch /mnt/tmp/mount/foo
touch: cannot touch '/mnt/tmp/mount/foo': Read-only file system
$ mount
[...]
127.0.0.1:~/tmp/test-nfs on /mnt/tmp type nfs4 (rw,...)
127.0.0.1:~/tmp/test-nfs/mount on /mnt/tmp/mount type nfs4 (rw,...)
(So the submount still appears rw – NFS doesn’t reevaluate when it
receives EROFS.)
On virtio-fs, it’s the same:
$ LANG=C sudo touch /mnt/mnt1
touch: cannot touch '/mnt/mnt1/foo': Read-only file system
$ mount
[...]
host on /mnt type virtiofs (rw,relatime)
none on /mnt/mnt1 type virtiofs (rw,relatime)
Max
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