Re: [PATCH v2] erofs: accept source file descriptor via fsconfig

On 2026/7/14 08:49, Aleksa Sarai wrote:
> On 2026-07-13, Giuseppe Scrivano <[email protected]> wrote:
>> thanks for the hints.
>>
>> I'll prepare a v3 if you are fine with the version below:
> 
> No worries, and this seems more reasonable at a first glance.
> 
>> diff --git a/fs/erofs/super.c b/fs/erofs/super.c
>> index 86fa5c6a0c70..72c85cc53085 100644
>> --- a/fs/erofs/super.c
>> +++ b/fs/erofs/super.c
> ...
>> @@ -437,6 +439,38 @@ static bool erofs_fc_set_dax_mode(struct fs_context *fc, unsigned int mode)
>>   	return false;
>>   }
>>   
>> +static int erofs_fc_parse_source(struct fs_context *fc,
>> +				 struct fs_parameter *param)
>> +{
>> +	struct erofs_sb_info *sbi = fc->s_fs_info;
>> +
>> +	if (fc->source || sbi->dif0.file)
>> +		return invalf(fc, "Multiple sources");
>> +
>> +	switch (param->type) {
>> +	case fs_value_is_string:
>> +		fc->source = param->string;
>> +		param->string = NULL;
>> +		return 0;
>> +	case fs_value_is_file: {
>> +		char *buf, *p;
>> +
>> +		sbi->dif0.file = get_file(param->file);
> 
> A very minor nit, but you can actually steal the file reference here
> with
> 
> 		sbi->dif0.file = no_free_ptr(param->file);
> 
> A few other places do this. (You'll also need to change the param->file
> reference below.)
> 
>> +		buf = kmalloc(PATH_MAX, GFP_KERNEL);
>> +		if (!buf)
>> +			return -ENOMEM;
>> +		p = file_path(param->file, buf, PATH_MAX);
>> +		fc->source = kstrdup(IS_ERR(p) ? "(fd)" : p, GFP_KERNEL);
> 
> I think that /proc/self/fd/%d would be a more useful name for debugging
> if file_path() fails (not that it is really possible here AFAICS). But
> I'm not really too fussed.

Not quite sure if we should get in agreement with the format of this
one in advance (IOWs, users use source_fd and how fc->source looks like;
since other fses may follow the same practice if source_fd becomes common
later) since it's a user-visible field and I believe we shouldn't treat
this one as a dontcare field as some pseudo fses (since those fses don't
rely on `fc->source` by design but typically EROFS can rely on.)

I hope Christian and others could share move thought on this part too
before I land this feature for the next cycle.

Thanks,
Gao Xiang


>