Re: [PATCH] erofs: fix file-backed mounts over FUSE

[Gao Xiang <hsiangkao@linux.alibaba.com>]

Hi Al,

On 2024/11/14 14:04, Al Viro wrote:
> On Thu, Nov 14, 2024 at 01:19:57PM +0800, Gao Xiang wrote:
> 
>> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
>> index 6355866220ff..43c89194d348 100644
>> --- a/fs/erofs/data.c
>> +++ b/fs/erofs/data.c
>> @@ -38,7 +38,10 @@ void *erofs_bread(struct erofs_buf *buf, erofs_off_t offset,
>>   	}
>>   	if (!folio || !folio_contains(folio, index)) {
>>   		erofs_put_metabuf(buf);
>> -		folio = read_mapping_folio(buf->mapping, index, NULL);
>> +		folio = buf->use_fp ?
>> +			read_mapping_folio(file_inode(buf->filp)->i_mapping,
>> +				index, buf->filp) :
>> +			read_mapping_folio(buf->mapping, index, NULL);
> 
> UGH...
> 
> 1) 'filp' is an atrocious identifier.  Please, don't perpetuate
> the piss-poor taste of AST - if you want to say 'file', say so.

ok.

> 
> 2) there's ->f_mapping; no need to go through the file_inode().

Yeah, thanks for the suggestion.

> 
> 3) AFAICS, (buf->kmap_type == EROFS_KMAP) == (buf->base != NULL).  What's
> the point of having that as a separate field?

Once buf->kmap_type has EROFS_KMAP and EROFS_KMAP_ATOMIC, but it
seems that it can be cleaned up now.

I will clean up later but it's a seperate story.

> 
> 4) Why bother with union?  Just have buf->file serve as your buf->use_fp
> and be done with that...

I'd like to leave `struct erofs_buf` as small as possible since
it's on stack.

Leave two fields for this are also ok for me anyway.

Thanks,
Gao Xiang