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[PATCH] writeback: fix range handling

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When a writeback_control's `start' and `end' fields are used to
indicate a one-byte-range starting at file offset zero, the required
values of .start=0,.end=0 mean that the ->writepages() implementation
has no way of telling that it is being asked to perform a range
request.  Because we're currently overloading (start == 0 && end == 0)
to mean "this is not a write-a-range request".

To make all this sane, the patch changes range of writeback_control.

So caller does: If it is calling ->writepages() to write pages, it
sets range (range_start/end or range_cyclic) always.

And if range_cyclic is true, ->writepages() thinks the range is
cyclic, otherwise it just uses range_start and range_end.

This patch does,

    - Add LLONG_MAX, LLONG_MIN, ULLONG_MAX to include/linux/kernel.h
      -1 is usually ok for range_end (type is long long). But, if someone did,

		range_end += val;		range_end is "val - 1"
		u64val = range_end >> bits;	u64val is "~(0ULL)"

      or something, they are wrong. So, this adds LLONG_MAX to avoid nasty
      things, and uses LLONG_MAX for range_end.

    - All callers of ->writepages() sets range_start/end or range_cyclic.

    - Fix updates of ->writeback_index. It seems already bit strange.
      If it starts at 0 and ended by check of nr_to_write, this last
      index may reduce chance to scan end of file.  So, this updates
      ->writeback_index only if range_cyclic is true or whole-file is
      scanned.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Nathan Scott <nathans@sgi.com>
Cc: Anton Altaparmakov <aia21@cantab.net>
Cc: Steven French <sfrench@us.ibm.com>
Cc: "Vladimir V. Saveliev" <vs@namesys.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
OGAWA Hirofumi
2006-06-23 02:03:26 -07:00
committed by Linus Torvalds
parent 4c91c3648c
commit 111ebb6e6f
9 changed files with 40 additions and 31 deletions
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22
fs/mpage.c
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@@ -707,9 +707,9 @@ mpage_writepages(struct address_space *mapping,
struct pagevec pvec;
int nr_pages;
pgoff_t index;
pgoff_t end = -1; /* Inclusive */
pgoff_t end; /* Inclusive */
int scanned = 0;
int is_range = 0;
int range_whole = 0;
if (wbc->nonblocking && bdi_write_congested(bdi)) {
wbc->encountered_congestion = 1;
@@ -721,16 +721,14 @@ mpage_writepages(struct address_space *mapping,
writepage = mapping->a_ops->writepage;
pagevec_init(&pvec, 0);
if (wbc->sync_mode == WB_SYNC_NONE) {
if (wbc->range_cyclic) {
index = mapping->writeback_index; /* Start from prev offset */
end = -1;
} else {
index = 0; /* whole-file sweep */
scanned = 1;
}
if (wbc->start || wbc->end) {
index = wbc->start >> PAGE_CACHE_SHIFT;
end = wbc->end >> PAGE_CACHE_SHIFT;
is_range = 1;
index = wbc->range_start >> PAGE_CACHE_SHIFT;
end = wbc->range_end >> PAGE_CACHE_SHIFT;
if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
range_whole = 1;
scanned = 1;
}
retry:
@@ -759,7 +757,7 @@ retry:
continue;
}
if (unlikely(is_range) && page->index > end) {
if (!wbc->range_cyclic && page->index > end) {
done = 1;
unlock_page(page);
continue;
@@ -810,7 +808,7 @@ retry:
index = 0;
goto retry;
}
if (!is_range)
if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
mapping->writeback_index = index;
if (bio)
mpage_bio_submit(WRITE, bio);