[PATCH] make bio->bi_max contain max vec entries

This changes the way we do pool lookups when freeing a bio.  Right now
we use bi_max as a handle into bvec_array[], to find the pool where it
came from.  This used to be just fine, because if you had a private bio,
you could specify your own destructor.  But now we have bio_add_page()
which also needs to know where the bio came from, or more precisely, it
needs to know how many entries the bio can hold.

So I've changed bi_max to bi_max_vecs, it now contains the number of vec
entries in the bio. Privately allocated bio's (or on stack) can now just
set bio->bi_max_vecs to reflect the max size. The pool index for the
default destructor is stored in the top bits of bi_flags.

1 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/bio.h b/include/linux/bio.h
index d3d75e2904ba..93ac8216aae4 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -81,8 +81,7 @@ struct bio {
 	unsigned short		bi_hw_segments;
 
 	unsigned int		bi_size;	/* residual I/O count */
-	unsigned int		bi_max;		/* max bvl_vecs we can hold,
-						   used as index into pool */
+	unsigned int		bi_max_vecs;	/* max bvl_vecs we can hold */
 
 	struct bio_vec		*bi_io_vec;	/* the actual vec list */
 
@@ -105,6 +104,14 @@ struct bio {
 #define bio_flagged(bio, flag)	((bio)->bi_flags & (1 << (flag)))
 
 /*
+ * top 4 bits of bio flags indicate the pool this bio came from
+ */
+#define BIO_POOL_BITS		(4)
+#define BIO_POOL_OFFSET		(BITS_PER_LONG - BIO_POOL_BITS)
+#define BIO_POOL_MASK		(1UL << BIO_POOL_OFFSET)
+#define BIO_POOL_IDX(bio)	((bio)->bi_flags >> BIO_POOL_OFFSET)	
+
+/*
  * bio bi_rw flags
  *
  * bit 0 -- read (not set) or write (set)