Re: [PATCH RFC] iomap: introduce IOMAP_TAIL

[Chao Yu <yuchao0@huawei.com>]

Hi Xiang,

On 2019/6/29 17:34, Gao Xiang wrote:
> Hi Chao,
> 
> On 2019/6/29 15:30, Chao Yu wrote:
>> Some filesystems like erofs/reiserfs have the ability to pack tail
>> data into metadata, however iomap framework can only support mapping
>> inline data with IOMAP_INLINE type, it restricts that:
>> - inline data should be locating at page #0.
>> - inline size should equal to .i_size
>> So we can not use IOMAP_INLINE to handle tail-packing case.
>>
>> This patch introduces new mapping type IOMAP_TAIL to map tail-packed
>> data for further use of erofs.
>>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>>  fs/iomap.c            | 22 ++++++++++++++++++++++
>>  include/linux/iomap.h |  1 +
>>  2 files changed, 23 insertions(+)
>>
>> diff --git a/fs/iomap.c b/fs/iomap.c
>> index 12654c2e78f8..ae7777ce77d0 100644
>> --- a/fs/iomap.c
>> +++ b/fs/iomap.c
>> @@ -280,6 +280,23 @@ iomap_read_inline_data(struct inode *inode, struct page *page,
>>  	SetPageUptodate(page);
>>  }
>>  
>> +static void
>> +iomap_read_tail_data(struct inode *inode, struct page *page,
>> +		struct iomap *iomap)
>> +{
>> +	size_t size = i_size_read(inode) & (PAGE_SIZE - 1);
>> +	void *addr;
>> +
>> +	if (PageUptodate(page))
>> +		return;
>> +
>> +	addr = kmap_atomic(page);
>> +	memcpy(addr, iomap->inline_data, size);
>> +	memset(addr + size, 0, PAGE_SIZE - size);
> 
> need flush_dcache_page(page) here for new page cache page since
> it's generic iomap code (althrough not necessary for x86, arm), I am not sure...
> see commit d2b2c6dd227b and c01778001a4f...

Thanks for your reminding, these all codes were copied from
iomap_read_inline_data(), so I think we need a separated patch to fix this issue
if necessary.

Thanks,

> 
> Thanks,
> Gao Xiang
> 
>> +	kunmap_atomic(addr);
>> +	SetPageUptodate(page);
>> +}
>> +
>>  static loff_t
>>  iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>>  		struct iomap *iomap)
>> @@ -298,6 +315,11 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>>  		return PAGE_SIZE;
>>  	}
>>  
>> +	if (iomap->type == IOMAP_TAIL) {
>> +		iomap_read_tail_data(inode, page, iomap);
>> +		return PAGE_SIZE;
>> +	}
>> +
>>  	/* zero post-eof blocks as the page may be mapped */
>>  	iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
>>  	if (plen == 0)
>> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
>> index 2103b94cb1bf..7e1ee48e3db7 100644
>> --- a/include/linux/iomap.h
>> +++ b/include/linux/iomap.h
>> @@ -25,6 +25,7 @@ struct vm_fault;
>>  #define IOMAP_MAPPED	0x03	/* blocks allocated at @addr */
>>  #define IOMAP_UNWRITTEN	0x04	/* blocks allocated at @addr in unwritten state */
>>  #define IOMAP_INLINE	0x05	/* data inline in the inode */
>> +#define IOMAP_TAIL	0x06	/* tail data packed in metdata */
>>  
>>  /*
>>   * Flags for all iomap mappings:
>>
> .
>