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authorDavid Howells <dhowells@redhat.com>2020-10-26 16:57:44 +0300
committerDavid Howells <dhowells@redhat.com>2020-10-29 16:53:04 +0300
commit65dd2d6072d393a3aa14ded8afa9a12f27d9c8ad (patch)
treed05f48830cd9ed16f4d45926b4a8a965fa503ee7 /fs/afs/write.c
parent185f0c7073bd5c78f86265f703f5daf1306ab5a7 (diff)
downloadlinux-65dd2d6072d393a3aa14ded8afa9a12f27d9c8ad.tar.xz
afs: Alter dirty range encoding in page->private
Currently, page->private on an afs page is used to store the range of dirtied data within the page, where the range includes the lower bound, but excludes the upper bound (e.g. 0-1 is a range covering a single byte). This, however, requires a superfluous bit for the last-byte bound so that on a 4KiB page, it can say 0-4096 to indicate the whole page, the idea being that having both numbers the same would indicate an empty range. This is unnecessary as the PG_private bit is clear if it's an empty range (as is PG_dirty). Alter the way the dirty range is encoded in page->private such that the upper bound is reduced by 1 (e.g. 0-0 is then specified the same single byte range mentioned above). Applying this to both bounds frees up two bits, one of which can be used in a future commit. This allows the afs filesystem to be compiled on ppc32 with 64K pages; without this, the following warnings are seen: ../fs/afs/internal.h: In function 'afs_page_dirty_to': ../fs/afs/internal.h:881:15: warning: right shift count >= width of type [-Wshift-count-overflow] 881 | return (priv >> __AFS_PAGE_PRIV_SHIFT) & __AFS_PAGE_PRIV_MASK; | ^~ ../fs/afs/internal.h: In function 'afs_page_dirty': ../fs/afs/internal.h:886:28: warning: left shift count >= width of type [-Wshift-count-overflow] 886 | return ((unsigned long)to << __AFS_PAGE_PRIV_SHIFT) | from; | ^~ Fixes: 4343d00872e1 ("afs: Get rid of the afs_writeback record") Signed-off-by: David Howells <dhowells@redhat.com>
Diffstat (limited to 'fs/afs/write.c')
-rw-r--r--fs/afs/write.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/afs/write.c b/fs/afs/write.c
index ea1768b3c0b5..1a49f5c89342 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -93,7 +93,7 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
/* We want to store information about how much of a page is altered in
* page->private.
*/
- BUILD_BUG_ON(PAGE_SIZE > 32768 && sizeof(page->private) < 8);
+ BUILD_BUG_ON(PAGE_SIZE - 1 > __AFS_PAGE_PRIV_MASK && sizeof(page->private) < 8);
page = grab_cache_page_write_begin(mapping, index, flags);
if (!page)