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Subject[PATCH -mm 5/10][RFC] aio: make blk_directIO use file_endio_t
Convert the internals of blkdev_direct_IO to use a generic endio function,
instead of directly calling aio_complete. This may also fix some bugs/races
in this code, for instance it checks bio->bi_size instead of assuming it's
zero, and it atomically accumulates the bytes_done counter (assuming that
the bio completion handler can't race with itself *might* be valid here, but
the direct-io code makes no such assumption). I'm also pretty sure that
the address_space->directIO functions aren't supposed to mess with the
iocb->ki_pos or ->ki_left.

---
diff -urpN -X dontdiff a/fs/block_dev.c b/fs/block_dev.c
--- a/fs/block_dev.c 2007-01-12 20:26:25.000000000 -0800
+++ b/fs/block_dev.c 2007-01-12 20:23:55.000000000 -0800
@@ -131,10 +131,32 @@ blkdev_get_block(struct inode *inode, se
return 0;
}

-static int blk_end_aio(struct bio *bio, unsigned int bytes_done, int error)
+struct bdev_aio {
+ atomic_t iocount; /* refcount */
+ atomic_t bytes_done; /* byte counter */
+ int err; /* error handling */
+ file_endio_t *endio; /* end I/O notify fn */
+ void *endio_data; /* notify fn private data */
+};
+
+static void blk_io_put(struct bdev_aio *io)
+{
+ if (!atomic_dec_and_test(&io->iocount))
+ return;
+
+ if (!io->endio)
+ return complete((struct completion*)io->endio_data);
+
+ io->endio(io->endio_data, atomic_read(&io->bytes_done), io->err);
+ kfree(io);
+}
+
+static int blk_bio_endio(struct bio *bio, unsigned int bytes_done, int error)
{
- struct kiocb *iocb = bio->bi_private;
- atomic_t *bio_count = &iocb->ki_bio_count;
+ struct bdev_aio *io = bio->bi_private;
+
+ if (bio->bi_size)
+ return 1;

if (bio_data_dir(bio) == READ)
bio_check_pages_dirty(bio);
@@ -143,16 +165,21 @@ static int blk_end_aio(struct bio *bio,
bio_put(bio);
}

- /* iocb->ki_nbytes stores error code from LLDD */
- if (error)
- iocb->ki_nbytes = -EIO;
-
- if (atomic_dec_and_test(bio_count))
- aio_complete(iocb, iocb->ki_left, iocb->ki_nbytes);
+ if (error)
+ io->err = error;
+ atomic_add(bytes_done, &io->bytes_done);

+ blk_io_put(io);
return 0;
}

+static void blk_io_init(struct bdev_aio *io)
+{
+ atomic_set(&io->iocount, 1);
+ atomic_set(&io->bytes_done, 0);
+ io->err = 0;
+}
+
#define VEC_SIZE 16
struct pvec {
unsigned short nr;
@@ -208,24 +235,33 @@ blkdev_direct_IO(int rw, struct kiocb *i

unsigned long addr; /* user iovec address */
size_t count; /* user iovec len */
- size_t nbytes = iocb->ki_nbytes = iocb->ki_left; /* total xfer size */
+ size_t nbytes; /* total xfer size */
loff_t size; /* size of block device */
struct bio *bio;
- atomic_t *bio_count = &iocb->ki_bio_count;
+ struct bdev_aio stack_io, *io;
+ file_endio_t *endio = aio_complete;
+ void *endio_data = iocb;
struct page *page;
struct pvec pvec;

pvec.nr = 0;
pvec.idx = 0;

+ io = &stack_io;
+ if (endio) {
+ io = kmalloc(sizeof(struct bdev_aio), GFP_KERNEL);
+ if (!io)
+ return -ENOMEM;
+ }
+ blk_io_init(io);
+
if (pos & blocksize_mask)
return -EINVAL;

+ nbytes = iov_length(iov, nr_segs);
size = i_size_read(inode);
- if (pos + nbytes > size) {
+ if (pos + nbytes > size)
nbytes = size - pos;
- iocb->ki_left = nbytes;
- }

/*
* check first non-zero iov alignment, the remaining
@@ -237,7 +273,6 @@ blkdev_direct_IO(int rw, struct kiocb *i
if (addr & blocksize_mask || count & blocksize_mask)
return -EINVAL;
} while (!count && ++seg < nr_segs);
- atomic_set(bio_count, 1);

while (nbytes) {
/* roughly estimate number of bio vec needed */
@@ -248,8 +283,8 @@ blkdev_direct_IO(int rw, struct kiocb *i
/* bio_alloc should not fail with GFP_KERNEL flag */
bio = bio_alloc(GFP_KERNEL, nvec);
bio->bi_bdev = I_BDEV(inode);
- bio->bi_end_io = blk_end_aio;
- bio->bi_private = iocb;
+ bio->bi_end_io = blk_bio_endio;
+ bio->bi_private = io;
bio->bi_sector = pos >> blkbits;
same_bio:
cur_off = addr & ~PAGE_MASK;
@@ -289,18 +324,27 @@ same_bio:
/* bio is ready, submit it */
if (rw == READ)
bio_set_pages_dirty(bio);
- atomic_inc(bio_count);
+ atomic_inc(&io->iocount);
submit_bio(rw, bio);
}

completion:
- iocb->ki_left -= nbytes;
- nbytes = iocb->ki_left;
- iocb->ki_pos += nbytes;
+ if (!endio) {
+ struct completion event;
+
+ init_completion(&event);
+ io->endio = NULL;
+ io->endio_data = &event;
+
+ if (!atomic_dec_and_test(&io->iocount))
+ wait_for_completion(&event);
+ return io->err ? io->err : atomic_read(&io->bytes_done);
+ }

- if (atomic_dec_and_test(bio_count))
- aio_complete(iocb, nbytes, 0);
+ io->endio = endio;
+ io->endio_data = endio_data;

+ blk_io_put(io);
return -EIOCBQUEUED;

backout:
@@ -316,7 +360,7 @@ backout:
* if no bio was submmitted, return the error code.
* otherwise, proceed with pending I/O completion.
*/
- if (atomic_read(bio_count) == 1)
+ if (atomic_read(&io->iocount) == 1)
return PTR_ERR(page);
goto completion;
}
-
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