[PATCH v5 3/4]xfs: xfs_seek_data() refinements with lookup data buffer offset from page cache.
Jie Liu
jeff.liu at oracle.com
Tue Jul 31 03:03:09 CDT 2012
On 07/31/12 08:06, Dave Chinner wrote:
> On Thu, Jul 26, 2012 at 11:32:50PM +0800, Jeff Liu wrote:
>> Search data buffer offset for given range from page cache.
>>
>> Signed-off-by: Jie Liu <jeff.liu at oracle.com>
>> Reviewed-by: Mark Tinguely <tinguely at sgi.com>
>> Reviewed-by: Christoph Hellwig <hch at lst.de>
>> Reviewed-by: Dave Chinner <dchinner at redhat.com>
>>
>> ---
>> fs/xfs/xfs_file.c | 88 ++++++++++++++++++++++++++++++++++++++++++-----------
>> 1 files changed, 70 insertions(+), 18 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
>> index 69965a4..b1158b3 100644
>> --- a/fs/xfs/xfs_file.c
>> +++ b/fs/xfs/xfs_file.c
>> @@ -1182,8 +1182,6 @@ xfs_seek_data(
>> struct inode *inode = file->f_mapping->host;
>> struct xfs_inode *ip = XFS_I(inode);
>> struct xfs_mount *mp = ip->i_mount;
>> - struct xfs_bmbt_irec map[2];
>> - int nmap = 2;
>> loff_t uninitialized_var(offset);
>> xfs_fsize_t isize;
>> xfs_fileoff_t fsbno;
>> @@ -1199,34 +1197,88 @@ xfs_seek_data(
>> goto out_unlock;
>> }
>>
>> - fsbno = XFS_B_TO_FSBT(mp, start);
>> -
>> /*
>> * Try to read extents from the first block indicated
>> * by fsbno to the end block of the file.
>> */
>> + fsbno = XFS_B_TO_FSBT(mp, start);
>> end = XFS_B_TO_FSB(mp, isize);
>> + for (;;) {
>> + struct xfs_bmbt_irec map[2];
>> + int nmap = 2;
>>
>> - error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
>> - XFS_BMAPI_ENTIRE);
>> - if (error)
>> - goto out_unlock;
>> + error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
>> + XFS_BMAPI_ENTIRE);
>> + if (error)
>> + goto out_unlock;
>>
>> - /*
>> - * Treat unwritten extent as data extent since it might
>> - * contains dirty data in page cache.
>> - */
>> - if (map[0].br_startblock != HOLESTARTBLOCK) {
>> - offset = max_t(loff_t, start,
>> - XFS_FSB_TO_B(mp, map[0].br_startoff));
>> - } else {
>> - if (nmap == 1) {
>> + /* No extents at given offset, must be beyond EOF */
>> + if (nmap == 0) {
>> error = ENXIO;
>> goto out_unlock;
>> }
>>
>> offset = max_t(loff_t, start,
>> - XFS_FSB_TO_B(mp, map[1].br_startoff));
>> + XFS_FSB_TO_B(mp, map[0].br_startoff));
>> + if (map[0].br_state == XFS_EXT_NORM &&
>> + !isnullstartblock(map[0].br_startblock))
>> + break;
>> + else {
>> + /*
>> + * Landed in an unwritten extent, try to lookup data
> Not correct - hole, delay or unwritten land here.
Will fix it.
>
>> + * buffer from the page cache before proceeding to
>> + * check the next extent map. It's a hole if nothing
>> + * was found.
>> + */
>> + if (map[0].br_startblock == DELAYSTARTBLOCK ||
>> + map[0].br_state == XFS_EXT_UNWRITTEN) {
>> + /* Probing page cache start from offset */
>> + if (xfs_find_get_desired_pgoff(inode, &map[0],
>> + DATA_OFF, &offset))
>> + break;
>> + }
> If is is a DELAYSTARTBLOCK, and it is within EOF, then it is
> guaranteed to contain data. There is no need for a page cache lookup
> to decide where the data starts - by definition the data starts at
> map[0].br_startblock. I think you can treat DELAYSTARTBLOCK exactly
> the same as allocated XFS_EXT_NORM extents.
>
> That means the logic is:
>
> if (map[0].br_state == XFS_EXT_NORM &&
> (!isnullstartblock(map[0].br_startblock) ||
> map[0].br_startblock == DELAYSTARTBLOCK)) {
> break;
> } else if (map[0].br_state == XFS_EXT_UNWRITTEN) {
> /* Probing page cache start from offset */
> if (xfs_find_get_desired_pgoff(inode, &map[0],
> DATA_OFF, &offset))
> break;
> } else {
> /*
> * If we find a hole in map[0] and nothing in map[1] it
> * probably means that we are reading after EOF.
> */
> .....
> }
>
> Which kills a level of indentation in the code....
Just done a quick test with above modifications, it works to me, thanks.
>
>
>> + /*
>> + * Found a hole in map[0] and nothing in map[1].
>> + * Probably means that we are reading after EOF.
>> + */
>> + if (nmap == 1) {
>> + error = ENXIO;
>> + goto out_unlock;
>> + }
>> +
>> + /*
>> + * We have two mappings, proceed to check map[1].
>> + */
>> + offset = max_t(loff_t, start,
>> + XFS_FSB_TO_B(mp, map[1].br_startoff));
>> + if (map[1].br_state == XFS_EXT_NORM &&
>> + !isnullstartblock(map[1].br_startblock))
>> + break;
>> + else {
>> + /*
>> + * map[1] is also an unwritten extent, lookup
>> + * data buffer from page cache now.
>> + */
>> + if (map[1].br_startblock == DELAYSTARTBLOCK ||
>> + map[1].br_state == XFS_EXT_UNWRITTEN) {
>> + if (xfs_find_get_desired_pgoff(inode,
>> + &map[1], DATA_OFF, &offset))
>> + break;
>> + }
>> + }
> And the if/elseif/else logic above can be repeated here.
>
>> + }
>> +
>> + /*
>> + * Nothing was found, proceed to the next round of search if
>> + * reading offset not beyond or hit EOF.
>> + */
>> + fsbno = map[1].br_startoff + map[1].br_blockcount;
>> + start = XFS_FSB_TO_B(mp, fsbno);
>> + if (start >= isize) {
>> + error = ENXIO;
>> + goto out_unlock;
>> + }
> Shouldn't this check be done at the start of the loop?
If put this check at the beginning of the loop, the code block would
looks like below:
isize = i_size_read(inode);
if (start >= isize) {
error = ENXIO;
goto out_unlock;
}
.......
for (;;) {
struct xfs_bmbt_irec map[2];
int nmap = 2;
if (start >= isize) {
error = ENXIO;
goto out_unlock;
}
error = xfs_bmapi_read(ip, fsbno, end - fsbno, map, &nmap,
XFS_BMAPI_ENTIRE);
if (error)
goto out_unlock;
/* No extents at given offset, must be beyond EOF */
if (nmap == 0) {
error = ENXIO;
goto out_unlock;
}
..........
.....
/*
* Nothing was found, proceed to the next round of
search if
* reading offset not beyond or hit EOF.
*/
fsbno = map[1].br_startoff + map[1].br_blockcount;
start = XFS_FSB_TO_B(mp, fsbno);
}
But we have a similar check up at the begnning of xfs_seek_data(), will
it looks a bit weird?
Thanks,
-Jeff
>
> Cheers,
>
> Dave.
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