UML mount failure with Linux 6.11

[Hongbo Li]

On 2024/11/13 9:23, Hongbo Li wrote:
> 
> 
> On 2024/11/13 4:10, Karel Zak wrote:
>>
>>   Hi,
>>
>> On Mon, Nov 11, 2024 at 09:16:18AM GMT, Hongbo Li wrote:
>>> We are discussing about the hostfs mount with new mount API in [1]. 
>>> And may
>>> need your help.
>>>
>>> After finishing the conversion to the new mount API for hostfs, it
>>> encountered a situation where the old version supported only one mount
>>> option, and the whole mount option was used as the root path (it is also
>>> valid for the path to contain commas). But when switching to the new 
>>> mount
>>> API, the option part will be split using commas (if I'm not mistaken, 
>>> this
>>> step would be done in libmount), which could potentially split a 
>>> complete
>>> path into multiple parts, and the call fsconfig syscall to set the mount
>>> options for underline filesystems. This is different from the original
>>> intention of hostfs. And this kind of situation is not common in other
>>> filesystems.
>>
>> The options has been always parsed by mount(8) and it's very fragile
>> to assume that kernel get as in the original order (etc.).
>>
>> For decades, commas have been supported in mount options. For example,
>> SeLinux uses them frequently in context settings. All you need to do
>> is use quotes, but be careful because the shell will strip them off.
>> Therefore, double quoting is required.
>>
> 
> Thanks for your reply!
> 
> If I'm not mistaken, we should add double quoting explicitly if we need 
> commas in mount options. However, it seems different for hostfs. For 
> example, with hostfs, if we use "mount -t hostfs none -o 
> /home/hostfs,dir /mnt" in the older interface, which can successfully 
> mount the host directory `/home/hostfs,dir`, then we should use "mount 
> -t hostfs none -o '"/home/hostfs,dir"' /mnt" in the new interface. If 
> that is the case, we should change the mount command which is hardcoded 
> in the original project.
Sorry for the disturbance. So am I right?

Thanks,
Hongbo

> 
> Thanks,
> Hongbo
> 
>>     mount -o 'rw,bbb="this,is,value",ccc'
>>
>> It's also supported in fstab, just use name="v,a,l,u,e"
>>
>> You can try it:
>>
>>   # strace -e fsconfig mount -t tmpfs -o 'rw,bbb="this,is,value",ccc' 
>> tmpfs /dontexist
>>
>>   fsconfig(3, FSCONFIG_SET_STRING, "source", "tmpfs", 0) = 0
>>   fsconfig(3, FSCONFIG_SET_FLAG, "rw", NULL, 0) = 0
>>   fsconfig(3, FSCONFIG_SET_STRING, "bbb", "this,is,value", 0) = -1 EINVAL
>>
>> You can see the expected result when using fsconfig().
>>
>>   Karel
>>
>>
> 
>