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authorBadari Pulavarty <pbadari@us.ibm.com>2006-03-26 01:38:00 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-26 08:57:01 -0800
commit205f87f6b342444f722e4559d33318686f7df2ca (patch)
tree61f32bb0582dde9fd62ee3d03ac3324b949b29e6 /include/linux
parentd48589bfad0e60bff0aa3f9e4875983f607bd44b (diff)
[PATCH] change buffer_head.b_size to size_t
Increase the size of the buffer_head b_size field (only) for 64 bit platforms. Update some old and moldy comments in and around the structure as well. The b_size increase allows us to perform larger mappings and allocations for large I/O requests from userspace, which tie in with other changes allowing the get_block_t() interface to map multiple blocks at once. Signed-off-by: Nathan Scott <nathans@sgi.com> Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/buffer_head.h19
1 files changed, 11 insertions, 8 deletions
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index da917ed096a..464f068f8b1 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -46,25 +46,28 @@ struct address_space;
typedef void (bh_end_io_t)(struct buffer_head *bh, int uptodate);
/*
- * Keep related fields in common cachelines. The most commonly accessed
- * field (b_state) goes at the start so the compiler does not generate
- * indexed addressing for it.
+ * Historically, a buffer_head was used to map a single block
+ * within a page, and of course as the unit of I/O through the
+ * filesystem and block layers. Nowadays the basic I/O unit
+ * is the bio, and buffer_heads are used for extracting block
+ * mappings (via a get_block_t call), for tracking state within
+ * a page (via a page_mapping) and for wrapping bio submission
+ * for backward compatibility reasons (e.g. submit_bh).
*/
struct buffer_head {
- /* First cache line: */
unsigned long b_state; /* buffer state bitmap (see above) */
struct buffer_head *b_this_page;/* circular list of page's buffers */
struct page *b_page; /* the page this bh is mapped to */
- atomic_t b_count; /* users using this block */
- u32 b_size; /* block size */
- sector_t b_blocknr; /* block number */
- char *b_data; /* pointer to data block */
+ sector_t b_blocknr; /* start block number */
+ size_t b_size; /* size of mapping */
+ char *b_data; /* pointer to data within the page */
struct block_device *b_bdev;
bh_end_io_t *b_end_io; /* I/O completion */
void *b_private; /* reserved for b_end_io */
struct list_head b_assoc_buffers; /* associated with another mapping */
+ atomic_t b_count; /* users using this buffer_head */
};
/*