Re: [RFC] write(2) semantics wrt return values and current position

[Junxiao Bi <junxiao.bi@oracle.com>]

On 04/09/2015 05:20 AM, Al Viro wrote:
> On Wed, Apr 08, 2015 at 09:57:37PM +0100, Al Viro wrote:
>> ... and having looked through old mail, there's _another_ breakage that
>> might have inspired that one; this one is mine - "ocfs2 syncs the wrong range".
>> It was syncing the wrong range with O_APPEND, all right, but after that
>> patch it was syncing the wrong range in _all_ cases.  What it should've
>> been doing instead is
>>                 ret = filemap_fdatawrite_range(file->f_mapping,
>> 					       iocb->ki_pos - written,
>>                                                iocb->ki_pos - 1);
>> ...
>>                         ret = filemap_fdatawait_range(file->f_mapping,
>> 						      iocb->ki_pos - written,
>>                                                       iocb->ki_pos - 1);

Looks like if generic_file_direct_write() return -EIOCBQUEUED and
IS_SYNC(inode) is true, the sync range is also wrong.


2385         if (direct_io) {
2386                 loff_t endbyte;
2387                 ssize_t written_buffered;
2388                 written = generic_file_direct_write(iocb, from, *ppos);
2389                 if (written < 0 || written == count) {
2390                         ret = written;
2391                         goto out_dio;
2392                 }

2443         if (((file->f_flags & O_DSYNC) && !direct_io) ||
IS_SYNC(inode) ||
2444             ((file->f_flags & O_DIRECT) && !direct_io)) {

The other two patches looks good.


Thanks,
Junxiao.
>>
>> Joseph, my apologies for missing your mail back in January - you are absolutely
>> correct, *ppos (aka iocb->ki_pos) _is_ changed.  Unlike pos, it can be used
>> to get the right range reliably (as above; pos, back when it existed,
>> hadn't been affected by generic_write_checks() call in what used to be
>> ocfs2_file_aio_write()), but the actual calculation had been completely
>> wrong.
>>
>> If that had contributed to confusion, my deep apologies...
> 
> Folks, could you please take a look through vfs.git#for-linus (the last
> three commits in there) and see if you are OK with those?
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