[PATCH] writeback: fix range handling
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>
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index e2b4ce1..487ea8b 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1079,9 +1079,9 @@
unsigned int bytes_written;
struct cifs_sb_info *cifs_sb;
int done = 0;
- pgoff_t end = -1;
+ pgoff_t end;
pgoff_t index;
- int is_range = 0;
+ int range_whole = 0;
struct kvec iov[32];
int len;
int n_iov = 0;
@@ -1122,16 +1122,14 @@
xid = GetXid();
pagevec_init(&pvec, 0);
- if (wbc->sync_mode == WB_SYNC_NONE)
+ if (wbc->range_cyclic) {
index = mapping->writeback_index; /* Start from prev offset */
- else {
- index = 0;
- scanned = 1;
- }
- if (wbc->start || wbc->end) {
- index = wbc->start >> PAGE_CACHE_SHIFT;
- end = wbc->end >> PAGE_CACHE_SHIFT;
- is_range = 1;
+ end = -1;
+ } else {
+ 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:
@@ -1167,7 +1165,7 @@
break;
}
- if (unlikely(is_range) && (page->index > end)) {
+ if (!wbc->range_cyclic && page->index > end) {
done = 1;
unlock_page(page);
break;
@@ -1271,7 +1269,7 @@
index = 0;
goto retry;
}
- if (!is_range)
+ if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
mapping->writeback_index = index;
FreeXid(xid);