On 09/28/2011 04:53 PM, Yongqiang Yang wrote:

On Wed, Sep 28, 2011 at 4:40 PM, Jeff Liu [off-list ref] wrote:

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On 09/28/2011 04:11 PM, Yongqiang Yang wrote:

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On Wed, Sep 28, 2011 at 4:02 PM, Jeff Liu [off-list ref] wrote:

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On 09/28/2011 03:21 PM, Yongqiang Yang wrote:

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On Wed, Sep 28, 2011 at 2:32 PM, Jeff Liu [off-list ref] wrote:

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Hello all,

This is the V2 for add SEEK_DATA/SEEK_HOLE support to ext4.
In V1, I copied all the codes regarding fetching delayed-extents out to
my seek callback function, it's stupid to duplicate the code blocks.

Now the idea is, since the delayed-extents is the main concern to search
extents for both fiemap and seek, so IMHO, it's better to consolidate
this procedure into a new function(get_delayed_extent() in my patch),
and call it in fiemap and seek call-back functions if necessary.  In
this way, when yongqiang's delayed-extents tree is ready, we only need
to modify the code block at get_delayed_extent() accordingly.

In addition, yongqiang has pointed out there might be a deadlock, but
per my understood, as the target inode already locked via i_mutex in
ext4_llseek() before, this lock can prevent any modification to the
file, and we call find_get_pages_tag() when trying to fetch the dirty
pages, this function using rcu read lock, it also safe to read.  So I
have no idea what's wrong, could anyone please kindly point me out in
this case?  I'm definitely a newbie to this list, sorry for my ignorant.

Ok.  There is no deadlock, fiemap releases i_data_sem before calling
get_delayed_extent().

BTW: It seems that there is a bug in fiemap according to code, I am
not sure which commit introduced it, delayed extents beyond last
allocated block are ignored.

Hmm... could you show me a bit more detailed info with the test scenario
if convenient? I can help testing, at least 3.1.0-rc2+ is works to me.

Could you test a file with map info like AAAADDDDDHHHHDDDD,
A-allocated block, D-deayed block, H-hole.  then filefrag -v and have
a look if extent map info is right.

Do you means, open a file, write something, fsync(), then write
something, seek to some position and write something again?

Yep.

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If so, looks the filefrag -v result is ok by waiting for a few seconds.

What do you mean waiting for a few seconds?

If run filefrag -v immediately against a just created file, the delayed
extents will not shown, we have to wait a little while until they are
really allocated IMHO.

Thanks,
-Jeff

Yongqiang.

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Thanks,
-Jeff

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Thanks,
Yongqiang.

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Also, upstream coreutils-cp(1) has been well tested for ext4, it could
be used for fiemap tests based on the extent_scan module:
http://git.savannah.gnu.org/cgit/coreutils.git/tree/src/extent-scan.c?h=next&id=b56b53bd70b1f8fa2b5a95d4569bb72a2419b5cd

Thanks,
-Jeff

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Yongqiang.

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Anyway, I'd like to post the revised for your guys review first.
In have split the modification to two patches this time, since I hope to
make it looks more convenient for the review purpose.

The 1st patch, remove the delayed-extents fetching procedure to a
function named as get_delayed_extent(), and modify the
ext4_ext_fiemap_cb() accordingly.

The 2nd path add the ext4_ext_seek_cb() to implement the
SEEK_HOLE/SEEK_DATA stuff based on previous code change.

Testing:
========
In addition to the test cases mentioned in V1, I also done another tests
through sunil's seek test program, please refer to:
http://oss.oracle.com/~smushran/seek_data/seek_test.c

To ensure the 1st patch does not cause regression issue on fiemap, I
have done some tests via cp(1) with fiemap copy support, the sparse file
used for this test is produced by:
python -c "f=open('./sptest', 'w'); [(f.seek(x) or f.write(str(x))) for
x in range(1, 1000000000, 99999)]; f.close()


Any feedback are appreciated!


Thanks,
-Jeff