On Wed, May 23, 2018 at 04:43:38PM +0200, Christoph Hellwig wrote:
> Simply use iomap_apply to iterate over the file and a submit a bio for
> each non-uptodate but mapped region and zero everything else. Note that
> as-is this can not be used for file systems with a blocksize smaller than
> the page size, but that support will be added later.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> fs/iomap.c | 194 +++++++++++++++++++++++++++++++++++++++++-
> include/linux/iomap.h | 4 +
> 2 files changed, 197 insertions(+), 1 deletion(-)
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index fa278ed338ce..78259a2249f4 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -1,6 +1,6 @@
> /*
> * Copyright (C) 2010 Red Hat, Inc.
> - * Copyright (c) 2016 Christoph Hellwig.
> + * Copyright (c) 2016-2018 Christoph Hellwig.
> *
> * This program is free software; you can redistribute it and/or modify it
> * under the terms and conditions of the GNU General Public License,
> @@ -18,6 +18,7 @@
> #include <linux/uaccess.h>
> #include <linux/gfp.h>
> #include <linux/mm.h>
> +#include <linux/mm_inline.h>
> #include <linux/swap.h>
> #include <linux/pagemap.h>
> #include <linux/pagevec.h>
> @@ -103,6 +104,197 @@ iomap_sector(struct iomap *iomap, loff_t pos)
> return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
> }
>
> +static void
> +iomap_read_end_io(struct bio *bio)
> +{
> + int error = blk_status_to_errno(bio->bi_status);
> + struct bio_vec *bvec;
> + int i;
> +
> + bio_for_each_segment_all(bvec, bio, i)
> + page_endio(bvec->bv_page, false, error);
> + bio_put(bio);
> +}
> +
> +static struct bio *
> +iomap_read_bio_alloc(struct iomap *iomap, sector_t sector, loff_t length)
> +{
> + int nr_vecs = (length + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + struct bio *bio = bio_alloc(GFP_NOFS, min(BIO_MAX_PAGES, nr_vecs));
> +
> + bio->bi_opf = REQ_OP_READ;
> + bio->bi_iter.bi_sector = sector;
> + bio_set_dev(bio, iomap->bdev);
> + bio->bi_end_io = iomap_read_end_io;
> + return bio;
> +}
> +
> +struct iomap_readpage_ctx {
> + struct page *cur_page;
> + bool cur_page_in_bio;
> + struct bio *bio;
> + struct list_head *pages;
> +};
> +
> +static loff_t
> +iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> + struct iomap *iomap)
> +{
> + struct iomap_readpage_ctx *ctx = data;
> + struct page *page = ctx->cur_page;
> + unsigned poff = pos & (PAGE_SIZE - 1);
> + unsigned plen = min_t(loff_t, PAGE_SIZE - poff, length);
> + bool is_contig = false;
> + sector_t sector;
> +
> + /* we don't support blocksize < PAGE_SIZE quite yet: */
> + WARN_ON_ONCE(pos != page_offset(page));
> + WARN_ON_ONCE(plen != PAGE_SIZE);
> +
> + if (iomap->type != IOMAP_MAPPED || pos >= i_size_read(inode)) {
> + zero_user(page, poff, plen);
> + SetPageUptodate(page);
> + goto done;
> + }
> +
> + ctx->cur_page_in_bio = true;
> +
> + /*
> + * Try to merge into a previous segment if we can.
> + */
> + sector = iomap_sector(iomap, pos);
> + if (ctx->bio && bio_end_sector(ctx->bio) == sector) {
> + if (__bio_try_merge_page(ctx->bio, page, plen, poff))
> + goto done;
> + is_contig = true;
> + }
> +
> + if (!ctx->bio || !is_contig || bio_full(ctx->bio)) {
> + if (ctx->bio)
> + submit_bio(ctx->bio);
> + ctx->bio = iomap_read_bio_alloc(iomap, sector, length);
> + }
> +
> + __bio_add_page(ctx->bio, page, plen, poff);
> +done:
> + return plen;
> +}
> +
> +int
> +iomap_readpage(struct page *page, const struct iomap_ops *ops)
> +{
> + struct iomap_readpage_ctx ctx = { .cur_page = page };
> + struct inode *inode = page->mapping->host;
> + unsigned poff;
> + loff_t ret;
> +
> + WARN_ON_ONCE(page_has_buffers(page));
> +
> + for (poff = 0; poff < PAGE_SIZE; poff += ret) {
> + ret = iomap_apply(inode, page_offset(page) + poff,
> + PAGE_SIZE - poff, 0, ops, &ctx,
> + iomap_readpage_actor);
> + if (ret <= 0) {
> + WARN_ON_ONCE(ret == 0);
> + SetPageError(page);
> + break;
> + }
> + }
> +
> + if (ctx.bio) {
> + submit_bio(ctx.bio);
> + WARN_ON_ONCE(!ctx.cur_page_in_bio);
> + } else {
> + WARN_ON_ONCE(ctx.cur_page_in_bio);
> + unlock_page(page);
> + }
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(iomap_readpage);
> +
> +static struct page *
> +iomap_next_page(struct inode *inode, struct list_head *pages, loff_t pos,
> + loff_t length, loff_t *done)
> +{
> + while (!list_empty(pages)) {
> + struct page *page = lru_to_page(pages);
> +
> + if (page_offset(page) >= (u64)pos + length)
> + break;
> +
> + list_del(&page->lru);
> + if (!add_to_page_cache_lru(page, inode->i_mapping, page->index,
> + GFP_NOFS))
I'm curious about this line -- if add_to_page_cache_lru returns an
error, why don't we want to send that back up the stack? Is the idea
that the page doesn't become uptodate and something else notices? It
seems a little odd that on error we just skip to the next page.
(If this /is/ correct then comment is needed here.)
--D
> + return page;
> +
> + *done += PAGE_SIZE;
> + put_page(page);
> + }
> +
> + return NULL;
> +}
> +
> +static loff_t
> +iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length,
> + void *data, struct iomap *iomap)
> +{
> + struct iomap_readpage_ctx *ctx = data;
> + loff_t done, ret;
> +
> + for (done = 0; done < length; done += ret) {
> + if (ctx->cur_page && ((pos + done) & (PAGE_SIZE - 1)) == 0) {
> + if (!ctx->cur_page_in_bio)
> + unlock_page(ctx->cur_page);
> + put_page(ctx->cur_page);
> + ctx->cur_page = NULL;
> + }
> + if (!ctx->cur_page) {
> + ctx->cur_page = iomap_next_page(inode, ctx->pages,
> + pos, length, &done);
> + if (!ctx->cur_page)
> + break;
> + ctx->cur_page_in_bio = false;
> + }
> + ret = iomap_readpage_actor(inode, pos + done, length - done,
> + ctx, iomap);
> + }
> +
> + return done;
> +}
> +
> +int
> +iomap_readpages(struct address_space *mapping, struct list_head *pages,
> + unsigned nr_pages, const struct iomap_ops *ops)
> +{
> + struct iomap_readpage_ctx ctx = { .pages = pages };
> + loff_t pos = page_offset(list_entry(pages->prev, struct page, lru));
> + loff_t last = page_offset(list_entry(pages->next, struct page, lru));
> + loff_t length = last - pos + PAGE_SIZE, ret = 0;
> +
> + while (length > 0) {
> + ret = iomap_apply(mapping->host, pos, length, 0, ops,
> + &ctx, iomap_readpages_actor);
> + if (ret <= 0) {
> + WARN_ON_ONCE(ret == 0);
> + goto done;
> + }
> + pos += ret;
> + length -= ret;
> + }
> + ret = 0;
> +done:
> + if (ctx.bio)
> + submit_bio(ctx.bio);
> + if (ctx.cur_page) {
> + if (!ctx.cur_page_in_bio)
> + unlock_page(ctx.cur_page);
> + put_page(ctx.cur_page);
> + }
> + WARN_ON_ONCE(!ret && !list_empty(ctx.pages));
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(iomap_readpages);
> +
> static void
> iomap_write_failed(struct inode *inode, loff_t pos, unsigned len)
> {
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index a044a824da85..7300d30ca495 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -9,6 +9,7 @@ struct fiemap_extent_info;
> struct inode;
> struct iov_iter;
> struct kiocb;
> +struct page;
> struct vm_area_struct;
> struct vm_fault;
>
> @@ -88,6 +89,9 @@ struct iomap_ops {
>
> ssize_t iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *from,
> const struct iomap_ops *ops);
> +int iomap_readpage(struct page *page, const struct iomap_ops *ops);
> +int iomap_readpages(struct address_space *mapping, struct list_head *pages,
> + unsigned nr_pages, const struct iomap_ops *ops);
> int iomap_file_dirty(struct inode *inode, loff_t pos, loff_t len,
> const struct iomap_ops *ops);
> int iomap_zero_range(struct inode *inode, loff_t pos, loff_t len,
> --
> 2.17.0
>
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