Re: [PATCH] virtiofsd: Show submounts

[Max Reitz]

On 30.04.20 10:58, Dr. David Alan Gilbert wrote:
> * Max Reitz (address@hidden) wrote:
>> On 29.04.20 16:57, Dr. David Alan Gilbert wrote:
>>> * Dr. David Alan Gilbert (address@hidden) wrote:
>>>> * Max Reitz (address@hidden) wrote:
>>>>> Currently, setup_mounts() bind-mounts the shared directory without
>>>>> MS_REC.  This makes all submounts disappear.
>>>>>
>>>>> Pass MS_REC so that the guest can see submounts again.
>>>>
>>>> Thanks!
>>>>
>>>>> Fixes: 3ca8a2b1c83eb185c232a4e87abbb65495263756
>>>>
>>>> Should this actually be 5baa3b8e95064c2434bd9e2f312edd5e9ae275dc ?
>>>>
>>>>> Signed-off-by: Max Reitz <address@hidden>
>>>>> ---
>>>>>  tools/virtiofsd/passthrough_ll.c | 2 +-
>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/tools/virtiofsd/passthrough_ll.c 
>>>>> b/tools/virtiofsd/passthrough_ll.c
>>>>> index 4c35c95b25..9d7f863e66 100644
>>>>> --- a/tools/virtiofsd/passthrough_ll.c
>>>>> +++ b/tools/virtiofsd/passthrough_ll.c
>>>>> @@ -2643,7 +2643,7 @@ static void setup_mounts(const char *source)
>>>>>      int oldroot;
>>>>>      int newroot;
>>>>>  
>>>>> -    if (mount(source, source, NULL, MS_BIND, NULL) < 0) {
>>>>> +    if (mount(source, source, NULL, MS_BIND | MS_REC, NULL) < 0) {
>>>>>          fuse_log(FUSE_LOG_ERR, "mount(%s, %s, MS_BIND): %m\n", source, 
>>>>> source);
>>>>>          exit(1);
>>>>>      }
>>>>
>>>> Do we want MS_SLAVE to pick up future mounts that might happenf rom the
>>>> host?
>>>> What's the interaction between this and the MS_REC|MS_SLAVE that we have
>>>> a few lines above for / ?
>>>
>>> Just to confirm something from vgoyal, and what had confused me about
>>> why we hadn't spotted this earlier.
>>>
>>> Even without this patch, the SLAVE stuff worked so if you start the
>>> daemon and *then* mount under the shared directory, the guest sees it
>>> with or without this patch.
>>
>> Hm, I don’t.  Do you really?
> 
> Yes! With your patch reverted:
> 
> Start virtiofsd, mount in the guest:
> 
> host:
> # ./virtiofsd --socket-path=/tmp/vhostqemu -o 
> source=/home/dgilbert/virtio-fs/fs  -o log_level=warn -o no_writeback
> 
> guest:
> # mount -t virtiofs myfs /sysroot

OK, for some reason I didn’t try to mount in the guest first, but did
the host mount after starting virtiofsd.

My mount test uses multiple mounts, and two of them I see mounted, but
three I still don’t see mounted.

Let me see whether I can come up with something reproducible that isn’t
a script.

[...]

> Maybe this is related to what Vivek said about default behaviours on
> systemd's, what does:
> 
> # findmnt -o +PROPAGATION
> TARGET    SOURCE         FSTYPE     OPTIONS                                   
>                                                PROPAGATION
> /         /dev/mapper/fedora_dgilbert--t580-root
> │                        xfs        
> rw,relatime,seclabel,attr2,inode64,logbufs=8,logbsize=32k,noquota             
>            shared
> 
> say for your source= directory?

I have Fedora, too, so pretty much the same.

Max

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