Two segbuf functions, nilfs_segbuf_write and nilfs_segbuf_wait, are
declared with the static storage class specifier, but their
implementations are not.

This fixes the discrepancy.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This moves iterator to submit write requests for a series of logs into
segbuf.c, and hides nilfs_segbuf_write() and nilfs_segbuf_wait() in
the file.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This separates wait function for submitted logs from the write
function nilfs_segctor_write().  A new list of segment buffers
"sc_write_logs" is added to hold logs under writing, and double
buffering is partially applied to hide io latency.

At this point, the double buffering is disabled for blocksize <
pagesize because page dirty flag is turned off during write and dirty
buffers are not properly collected for pages crossing over segments.

To receive full benefit of the double buffering, further refinement is
needed to move the io wait outside the lock section of log writer.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This adds a few iterator functions for segment buffers to make it easy
to handle multiple series of logs.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

Hides nilfs_write_info struct and nilfs_segbuf_prepare_write function
in segbuf.c to simplify the interface of nilfs_segbuf_write function.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This moves io status variables in nilfs_write_info struct to
nilfs_segment_buffer struct.

This is a preparation to hide nilfs_write_info in segment buffer code.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

Previously, log writer had possibility to set an io error flag on
segments even in case of memory allocation failure.

This fixes the issue.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

Alberto Bertogli advised me about bio_alloc() use in nilfs:
On Sat, 13 Jun 2009 22:52:40 -0300, Alberto Bertogli wrote:
> By the way, those bio_alloc()s are using GFP_NOWAIT but it looks
> like they could use at least GFP_NOIO or GFP_NOFS, since the caller
> can (and sometimes do) sleep. The only caller is nilfs_submit_bh(),
> which calls nilfs_submit_seg_bio() which can sleep calling
> wait_for_completion().

This takes in the comment and replaces the use of GFP_NOWAIT flag with
GFP_NOIO.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This sets BIO_RW_UNPLUG flag on the last bio of each segment during
write.  The last bio should be unplugged immediately because the
caller waits for the completion after the submission.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

This will clean up the removal list of segments and the related
functions from segment.c and ioctl.c, which have hurt code
readability.

This elimination is applied by using nilfs_sufile_updatev() previously
introduced in the patch ("nilfs2: add sufile function that can modify
multiple segment usages").
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

will reduce some lines of segment constructor.  Previously, the state was
complexly controlled through a list of segments in order to keep
consistency in meta data of usage state of segments.  Instead, this
presents ``calculated'' active flags to userland cleaner program and stop
maintaining its real flag on disk.

Only by this fake flag, the cleaner cannot exactly know if each segment is
reclaimable or not.  However, the recent extension of nilfs_sustat ioctl
struct (nilfs2-extend-nilfs_sustat-ioctl-struct.patch) can prevent the
cleaner from reclaiming in-use segment wrongly.

So, now I can apply this for simplification.
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This adds the segment buffer which is used to constuct logs.

[akpm@linux-foundation.org: BIO_RW_SYNC got removed]
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>