Incorrect error message from erofs "backed by file" in 6.12-rc

[Gao Xiang]

On 2024/10/8 16:46, Christian Brauner wrote:
> On Tue, Oct 08, 2024 at 10:13:31AM GMT, Gao Xiang wrote:
>> Hi Christian,
>>
>> On 2024/10/7 19:35, Christian Brauner wrote:
>>> On Sat, Oct 05, 2024 at 10:41:10PM GMT, Gao Xiang wrote:
>>
>> ...
>>
>>>>
>>>> Hi Christian, if possible, could you give some other
>>>> idea to handle this case better? Many thanks!
>>
>> Thanks for the reply!
>>
>>>
>>> (1) Require that the path be qualified like:
>>>
>>>       fsconfig(<fd>, FSCONFIG_SET_STRING, "source", "file:/home/lis/src/mountcfs/cfs", 0)
>>>
>>>       and match on it in either erofs_*_get_tree() or by adding a custom
>>>       function for the Opt_source/"source" parameter.
>>
>> IMHO, Users could create names with the prefix `file:`,
>> it's somewhat strange to define a fixed prefix by the
>> definition of source path fc->source.
>>
>> Although there could be some escape character likewise
>> way, but I'm not sure if it's worthwhile to work out
>> this in kernel.
>>
>>>
>>> (2) Add a erofs specific "source-file" mount option. IOW, check that
>>>       either "source-file" or "source" was specified but not both. You
>>>       could even set fc->source to "source-file" value and fail if
>>>       fc->source is already set. You get the idea.
>>
>> I once thought to add a new mount option too, yet from
>> the user perpertive, I think users may not care about
>> the source type of an arbitary path, and the kernel also
>> can parse the type of the source path directly... so..
>>
>>
>> So.. I wonder if it's possible to add a new VFS interface
>> like get_tree_bdev_by_dev() for filesystems to specify a
>> device number rather than hardcoded hard-coded source path
>> way, e.g. I could see the potential benefits other than
>> the EROFS use case:
>>
>>   - Filesystems can have other ways to get a bdev-based sb
>>     in addition to the current hard-coded source path way;
>>
>>   - Some pseudo fs can use this way to generate a fs from a
>>     bdev.
>>
>>   - Just like get_tree_nodev(), it doesn't strictly tie to
>>     fc->source too.
>>
>> Also EROFS could lookup_bdev() (this kAPI is already
>> exported) itself to check if it uses get_tree_bdev_by_dev()
>> or get_tree_nodev()... Does it sounds good?  Many thanks!
> 
> Sounds fair to me.

Okay, thanks! Let me submit patches for this.

Thanks,
Gao Xiang