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 | 195 +++++++++++++++++++++++++++++++++++++++++-
include/linux/iomap.h | 4 +
2 files changed, 198 insertions(+), 1 deletion(-)
diff --git a/fs/iomap.c b/fs/iomap.c
index 049e0c4aacac..967bd31540fe 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>
@@ -102,6 +103,198 @@ iomap_sector(struct iomap *iomap, loff_t pos)
return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
}
+static inline bool
+iomap_block_needs_zeroing(struct inode *inode, loff_t pos, struct iomap *iomap)
+{
+ return iomap->type != IOMAP_MAPPED || pos > i_size_read(inode);
+}
+
+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_block_needs_zeroing(inode, pos, iomap)) {
+ 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) {
+ SetPageError(page);
+ break;
+ }
+ }
+
+ if (ctx.bio)
+ submit_bio(ctx.bio);
+ else
+ 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 end,
+ loff_t *done)
+{
+ while (!list_empty(pages)) {
+ struct page *page = lru_to_page(pages);
+
+ if (page_offset(page) >= end)
+ break;
+
+ list_del(&page->lru);
+ if (!add_to_page_cache_lru(page, inode->i_mapping, page->index,
+ GFP_NOFS))
+ 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)
+ break;
+ pos += ret;
+ length -= ret;
+ }
+
+ ret = 0;
+
+ 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 07f73224c38b..4710789620e7 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;
@@ -83,6 +84,9 @@ 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
