Re: [PATCH 3/3] Btrfs: add basic DIO read support

[Christoph Hellwig <hch@infradead.org>]

> +struct btrfs_dio_private {
> +	struct inode *inode;
> +	u64 logical_offset;
> +	u32 *csums;
> +	void *private;
> +};
> +
> +static void btrfs_endio_direct(struct bio *bio, int err)
> +{
> +	struct bio_vec *bvec_end = bio->bi_io_vec + bio->bi_vcnt - 1;
> +	struct bio_vec *bvec = bio->bi_io_vec;
> +	struct btrfs_dio_private *dip = bio->bi_private;
> +	struct inode *inode = dip->inode;
> +	struct btrfs_root *root = BTRFS_I(inode)->root;
> +	u64 start;
> +	u32 *private = dip->csums;
> +
> +	start = dip->logical_offset;
> +	do {
> +		if (!(BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)) {
> +			struct page *page = bvec->bv_page;
> +			char *kaddr;
> +			u32 csum = ~(u32)0;
> +
> +			kaddr = kmap_atomic(page, KM_USER0);

KM_USER0 seems wrong given that the bio completion callback can and
usually will be called from some kind of IRQ context.

> +	ret = blockdev_direct_IO_own_submit(rw, iocb, inode, NULL, iov,
> +					    offset, nr_segs,
> +					    btrfs_get_blocks_direct,
> +					    btrfs_submit_direct);

Don't you need to do some alignment checks of your own given that you
don't pass in a block device?

Btw, passing in the bdev here is a really horrible API, I'd much rather
move this to the callers..

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