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Date: Wed, 25 Mar 2015 15:23:48 +0800
From: Ming Lei <ming.lei@...onical.com>
To: Christoph Hellwig <hch@....de>
Cc: Jens Axboe <axboe@...com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Al Viro <viro@...iv.linux.org.uk>,
Maxim Patlasov <mpatlasov@...allels.com>
Subject: Re: [PATCH 0/3] block: loop: switch to VFS ITER_BVEC
On Wed, Mar 25, 2015 at 2:01 AM, Christoph Hellwig <hch@....de> wrote:
> On Tue, Mar 24, 2015 at 06:53:07PM +0800, Ming Lei wrote:
>> If you have better one, please just ignore this patchset.
>
> Here is a straight forward port of my old one. It's got light testing but
> still could use a better description and a split up:
>
> ---
> From a45b5053db5908954d340b05ef8a23e1ca43010a Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@....de>
> Date: Fri, 16 Jan 2015 15:06:03 +0100
> Subject: loop: convert to vfs_iter_read/write
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
> drivers/block/loop.c | 291 +++++++++++++++++++++------------------------------
> 1 file changed, 119 insertions(+), 172 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index d1f168b..68974b2 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -87,28 +87,6 @@ static int part_shift;
>
> static struct workqueue_struct *loop_wq;
>
> -/*
> - * Transfer functions
> - */
> -static int transfer_none(struct loop_device *lo, int cmd,
> - struct page *raw_page, unsigned raw_off,
> - struct page *loop_page, unsigned loop_off,
> - int size, sector_t real_block)
> -{
> - char *raw_buf = kmap_atomic(raw_page) + raw_off;
> - char *loop_buf = kmap_atomic(loop_page) + loop_off;
> -
> - if (cmd == READ)
> - memcpy(loop_buf, raw_buf, size);
> - else
> - memcpy(raw_buf, loop_buf, size);
> -
> - kunmap_atomic(loop_buf);
> - kunmap_atomic(raw_buf);
> - cond_resched();
> - return 0;
> -}
> -
> static int transfer_xor(struct loop_device *lo, int cmd,
> struct page *raw_page, unsigned raw_off,
> struct page *loop_page, unsigned loop_off,
> @@ -147,7 +125,6 @@ static int xor_init(struct loop_device *lo, const struct loop_info64 *info)
>
> static struct loop_func_table none_funcs = {
> .number = LO_CRYPT_NONE,
> - .transfer = transfer_none,
> };
>
> static struct loop_func_table xor_funcs = {
> @@ -214,206 +191,169 @@ lo_do_transfer(struct loop_device *lo, int cmd,
> struct page *lpage, unsigned loffs,
> int size, sector_t rblock)
> {
> - if (unlikely(!lo->transfer))
> + int ret;
> +
> + ret = lo->transfer(lo, cmd, rpage, roffs, lpage, loffs, size, rblock);
> + if (likely(!ret))
> return 0;
>
> - return lo->transfer(lo, cmd, rpage, roffs, lpage, loffs, size, rblock);
> + printk_ratelimited(KERN_ERR
> + "loop: Transfer error at byte offset %llu, length %i.\n",
> + (unsigned long long)rblock << 9, size);
> + return ret;
> }
>
> -/**
> - * __do_lo_send_write - helper for writing data to a loop device
> - *
> - * This helper just factors out common code between do_lo_send_direct_write()
> - * and do_lo_send_write().
> - */
> -static int __do_lo_send_write(struct file *file,
> - u8 *buf, const int len, loff_t pos)
> +static int lo_write_bvec(struct file *file, struct bio_vec *bvec, loff_t *ppos)
> {
> + struct iov_iter i;
> ssize_t bw;
> - mm_segment_t old_fs = get_fs();
> +
> + iov_iter_bvec(&i, ITER_BVEC, bvec, 1, bvec->bv_len);
>
> file_start_write(file);
> - set_fs(get_ds());
> - bw = file->f_op->write(file, buf, len, &pos);
> - set_fs(old_fs);
> + bw = vfs_iter_write(file, &i, ppos);
This patch moves to support ->read_iter/->write_iter only, which
might cause regression for backing file without defining read/write
iter callback.
> file_end_write(file);
> - if (likely(bw == len))
> +
> + if (likely(bw == bvec->bv_len))
> return 0;
> - printk_ratelimited(KERN_ERR "loop: Write error at byte offset %llu, length %i.\n",
> - (unsigned long long)pos, len);
> +
> + printk_ratelimited(KERN_ERR
> + "loop: Write error at byte offset %llu, length %i.\n",
> + (unsigned long long)*ppos, bvec->bv_len);
> if (bw >= 0)
> bw = -EIO;
> return bw;
> }
>
> -/**
> - * do_lo_send_direct_write - helper for writing data to a loop device
> - *
> - * This is the fast, non-transforming version that does not need double
> - * buffering.
> - */
> -static int do_lo_send_direct_write(struct loop_device *lo,
> - struct bio_vec *bvec, loff_t pos, struct page *page)
> +static int lo_write_simple(struct loop_device *lo, struct request *rq,
> + loff_t pos)
> {
> - ssize_t bw = __do_lo_send_write(lo->lo_backing_file,
> - kmap(bvec->bv_page) + bvec->bv_offset,
> - bvec->bv_len, pos);
> - kunmap(bvec->bv_page);
> - cond_resched();
> - return bw;
> + struct bio_vec bvec;
> + struct req_iterator iter;
> + int ret = 0;
> +
> + rq_for_each_segment(bvec, rq, iter) {
> + ret = lo_write_bvec(lo->lo_backing_file, &bvec, &pos);
> + if (ret < 0)
> + break;
> + cond_resched();
> + }
> +
> + return ret;
> }
>
> -/**
> - * do_lo_send_write - helper for writing data to a loop device
> - *
> +/*
> * This is the slow, transforming version that needs to double buffer the
> * data as it cannot do the transformations in place without having direct
> * access to the destination pages of the backing file.
> */
> -static int do_lo_send_write(struct loop_device *lo, struct bio_vec *bvec,
> - loff_t pos, struct page *page)
> -{
> - int ret = lo_do_transfer(lo, WRITE, page, 0, bvec->bv_page,
> - bvec->bv_offset, bvec->bv_len, pos >> 9);
> - if (likely(!ret))
> - return __do_lo_send_write(lo->lo_backing_file,
> - page_address(page), bvec->bv_len,
> - pos);
> - printk_ratelimited(KERN_ERR "loop: Transfer error at byte offset %llu, "
> - "length %i.\n", (unsigned long long)pos, bvec->bv_len);
> - if (ret > 0)
> - ret = -EIO;
> - return ret;
> -}
> -
> -static int lo_send(struct loop_device *lo, struct request *rq, loff_t pos)
> +static int lo_write_transfer(struct loop_device *lo, struct request *rq,
> + loff_t pos)
> {
> - int (*do_lo_send)(struct loop_device *, struct bio_vec *, loff_t,
> - struct page *page);
> - struct bio_vec bvec;
> + struct bio_vec bvec, b;
> struct req_iterator iter;
> - struct page *page = NULL;
> + struct page *page;
> int ret = 0;
>
> - if (lo->transfer != transfer_none) {
> - page = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
> - if (unlikely(!page))
> - goto fail;
> - kmap(page);
> - do_lo_send = do_lo_send_write;
> - } else {
> - do_lo_send = do_lo_send_direct_write;
> - }
> + page = alloc_page(GFP_NOIO);
> + if (unlikely(!page))
> + return -ENOMEM;
>
> rq_for_each_segment(bvec, rq, iter) {
> - ret = do_lo_send(lo, &bvec, pos, page);
> + ret = lo_do_transfer(lo, WRITE, page, 0, bvec.bv_page,
> + bvec.bv_offset, bvec.bv_len, pos >> 9);
> + if (unlikely(ret))
> + break;
> +
> + b.bv_page = page;
> + b.bv_offset = 0;
> + b.bv_len = bvec.bv_len;
> + ret = lo_write_bvec(lo->lo_backing_file, &b, &pos);
> if (ret < 0)
> break;
> - pos += bvec.bv_len;
> }
> - if (page) {
> - kunmap(page);
> - __free_page(page);
> - }
> -out:
> +
> + __free_page(page);
> return ret;
> -fail:
> - printk_ratelimited(KERN_ERR "loop: Failed to allocate temporary page for write.\n");
> - ret = -ENOMEM;
> - goto out;
> }
>
> -struct lo_read_data {
> - struct loop_device *lo;
> - struct page *page;
> - unsigned offset;
> - int bsize;
> -};
> +static int lo_read_simple(struct loop_device *lo, struct request *rq,
> + loff_t pos)
> +{
> + struct bio_vec bvec;
> + struct req_iterator iter;
> + struct iov_iter i;
> + ssize_t len;
>
> -static int
> -lo_splice_actor(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
> - struct splice_desc *sd)
> -{
> - struct lo_read_data *p = sd->u.data;
> - struct loop_device *lo = p->lo;
> - struct page *page = buf->page;
> - sector_t IV;
> - int size;
> -
> - IV = ((sector_t) page->index << (PAGE_CACHE_SHIFT - 9)) +
> - (buf->offset >> 9);
> - size = sd->len;
> - if (size > p->bsize)
> - size = p->bsize;
> -
> - if (lo_do_transfer(lo, READ, page, buf->offset, p->page, p->offset, size, IV)) {
> - printk_ratelimited(KERN_ERR "loop: transfer error block %ld\n",
> - page->index);
> - size = -EINVAL;
> - }
> + rq_for_each_segment(bvec, rq, iter) {
> + iov_iter_bvec(&i, ITER_BVEC, &bvec, 1, bvec.bv_len);
> + len = vfs_iter_read(lo->lo_backing_file, &i, &pos);
> + if (len < 0)
> + return len;
>
> - flush_dcache_page(p->page);
> + flush_dcache_page(bvec.bv_page);
>
> - if (size > 0)
> - p->offset += size;
> + if (len != bvec.bv_len) {
> + struct bio *bio;
>
> - return size;
> -}
> + __rq_for_each_bio(bio, rq)
> + zero_fill_bio(bio);
> + break;
> + }
> + cond_resched();
> + }
>
> -static int
> -lo_direct_splice_actor(struct pipe_inode_info *pipe, struct splice_desc *sd)
> -{
> - return __splice_from_pipe(pipe, sd, lo_splice_actor);
> + return 0;
> }
>
> -static ssize_t
> -do_lo_receive(struct loop_device *lo,
> - struct bio_vec *bvec, int bsize, loff_t pos)
> +static int lo_read_transfer(struct loop_device *lo, struct request *rq,
> + loff_t pos)
> {
> - struct lo_read_data cookie;
> - struct splice_desc sd;
> - struct file *file;
> - ssize_t retval;
> -
> - cookie.lo = lo;
> - cookie.page = bvec->bv_page;
> - cookie.offset = bvec->bv_offset;
> - cookie.bsize = bsize;
> + struct bio_vec bvec, b;
> + struct req_iterator iter;
> + struct iov_iter i;
> + struct page *page;
> + ssize_t len;
> + int ret = 0;
>
> - sd.len = 0;
> - sd.total_len = bvec->bv_len;
> - sd.flags = 0;
> - sd.pos = pos;
> - sd.u.data = &cookie;
> + page = alloc_page(GFP_NOIO);
> + if (unlikely(!page))
> + return -ENOMEM;
The above page allocation is one code duplication.
>
> - file = lo->lo_backing_file;
> - retval = splice_direct_to_actor(file, &sd, lo_direct_splice_actor);
> + rq_for_each_segment(bvec, rq, iter) {
> + loff_t offset = pos;
>
> - return retval;
> -}
> + b.bv_page = page;
> + b.bv_offset = 0;
> + b.bv_len = bvec.bv_len;
>
> -static int
> -lo_receive(struct loop_device *lo, struct request *rq, int bsize, loff_t pos)
> -{
> - struct bio_vec bvec;
> - struct req_iterator iter;
> - ssize_t s;
> + iov_iter_bvec(&i, ITER_BVEC, &b, 1, b.bv_len);
> + len = vfs_iter_read(lo->lo_backing_file, &i, &pos);
> + if (len < 0) {
> + ret = len;
> + goto out_free_page;
> + }
>
> - rq_for_each_segment(bvec, rq, iter) {
> - s = do_lo_receive(lo, &bvec, bsize, pos);
> - if (s < 0)
> - return s;
> + ret = lo_do_transfer(lo, READ, page, 0, bvec.bv_page,
> + bvec.bv_offset, len, offset >> 9);
> + if (ret)
> + goto out_free_page;
> +
> + flush_dcache_page(bvec.bv_page);
>
> - if (s != bvec.bv_len) {
> + if (len != bvec.bv_len) {
> struct bio *bio;
>
> __rq_for_each_bio(bio, rq)
> zero_fill_bio(bio);
> break;
> }
both flush_fdcache_page and zero_fill_bio are code duplication too.
> - pos += bvec.bv_len;
> }
> - return 0;
> +
> + ret = 0;
> +out_free_page:
> + __free_page(page);
> + return ret;
> }
Free page is code duplication too.
>
> static int lo_discard(struct loop_device *lo, struct request *rq, loff_t pos)
> @@ -462,10 +402,17 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
> ret = lo_req_flush(lo, rq);
> else if (rq->cmd_flags & REQ_DISCARD)
> ret = lo_discard(lo, rq, pos);
> + else if (lo->transfer)
> + ret = lo_write_transfer(lo, rq, pos);
> else
> - ret = lo_send(lo, rq, pos);
> - } else
> - ret = lo_receive(lo, rq, lo->lo_blocksize, pos);
> + ret = lo_write_simple(lo, rq, pos);
> +
> + } else {
> + if (lo->transfer)
> + ret = lo_read_transfer(lo, rq, pos);
> + else
> + ret = lo_read_simple(lo, rq, pos);
> + }
IMO, lo_read/write_transfer and lo_read/write_simple can be
merged to avoid code duplication, since the logic for handling
lo->transfer in read/write is quite simple.
>
> return ret;
> }
> @@ -786,7 +733,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
> lo->lo_device = bdev;
> lo->lo_flags = lo_flags;
> lo->lo_backing_file = file;
> - lo->transfer = transfer_none;
> + lo->transfer = NULL;
> lo->ioctl = NULL;
> lo->lo_sizelimit = 0;
> lo->old_gfp_mask = mapping_gfp_mask(mapping);
> --
> 1.9.1
>
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