On 08/21/2014 05:05 PM, Ivan Shapovalov wrote:
On Thursday 21 August 2014 at 00:30:45, Edward Shishkin wrote:
On 08/20/2014 10:34 PM, Ivan Shapovalov wrote:
On Wednesday 20 August 2014 at 01:39:42, Edward Shishkin wrote:
On 08/20/2014 12:32 AM, Ivan Shapovalov wrote:
From `git log` I've seen that VFS people intend to replace ->aio_read() and
->aio_write() of struct file_operations with new methods ->read_iter() and
->write_iter().
(Along with a couple of related new helpers, differing from previous just in
calling _iter methods instead of aio_ ones.)
From other filesystems it seems that these are simple drop-in replacements
(however, well, I have zero familiarity with VFS). So here is a question:
is there any intentional reason that generic_file_aio_write() is not used
in reiser4?
Currently reiser4 is a set of two filesystems which differ in methods
of handling regular files. For VFS we provide "dispatchers", which pass
management to appropriate plugin (UNIX_FILE or CRYPTCOMPRESS).
UNIX_FILE plugin doesn't use generic write for performance reasons
(I'll try to find the respective mailing thread). CRYPTCOMPRESS doesn't
use it for compatibility reasons: I don't know how how to rewrite it
gracefully using the generic write method.
Edward.
Thanks for explanation! So, does this patch make any sense?
I haven't looked at this carefully yet, but likely it is correct.
Thanks,
Edward.
I have looked at VFS changes 3.15->3.16.
generic_file_aio_read() was replaced with generic_file_read_iter()
Respectively, all its users (including us) now call ->read_iter().
Since we don't implement our own ->aio_read(), we should use
new_sync_read() instead of do_sync_read().
So, everything looks OK with our read/write.
Turned out it isn't.. The iter_file_splice_write() requires ->write_iter
to be set, or a NULL dereference happens.
At first I've thought that we're out of luck and will need to use the fallback
splice implementation (default_file_splice_write), but just setting
->write_iter to generic_file_write_iter strangely worked.
(By "it works" I mean "splice finishes successfully and does not cause data
corruptions").
Could you please comment on this? :)
generic_file_splice_write() did:
->write_begin()
memcpy();
->write_end()
iter_file_splice_write() with generic_file_write_iter() does:
->write_begin()
copy_from_user();
->write_end()
So the question is why copy_from_user() works instead
of memcpy()? TBH, I don't know. If interesting, ask VFS
folks and tell us then ;)
Thanks,
Edward.
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