fs: introduce iomap infrastructure
Add infrastructure for multipage buffered writes. This is implemented
using an main iterator that applies an actor function to a range that
can be written.
This infrastucture is used to implement a buffered write helper, one
to zero file ranges and one to implement the ->page_mkwrite VM
operations. All of them borrow a fair amount of code from fs/buffers.
for now by using an internal version of __block_write_begin that
gets passed an iomap and builds the corresponding buffer head.
The file system is gets a set of paired ->iomap_begin and ->iomap_end
calls which allow it to map/reserve a range and get a notification
once the write code is finished with it.
Based on earlier code from Dave Chinner.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
diff --git a/fs/buffer.c b/fs/buffer.c
index 754813a..228288a 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -21,6 +21,7 @@
#include <linux/kernel.h>
#include <linux/syscalls.h>
#include <linux/fs.h>
+#include <linux/iomap.h>
#include <linux/mm.h>
#include <linux/percpu.h>
#include <linux/slab.h>
@@ -1891,8 +1892,62 @@
}
EXPORT_SYMBOL(page_zero_new_buffers);
-int __block_write_begin(struct page *page, loff_t pos, unsigned len,
- get_block_t *get_block)
+static void
+iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
+ struct iomap *iomap)
+{
+ loff_t offset = block << inode->i_blkbits;
+
+ bh->b_bdev = iomap->bdev;
+
+ /*
+ * Block points to offset in file we need to map, iomap contains
+ * the offset at which the map starts. If the map ends before the
+ * current block, then do not map the buffer and let the caller
+ * handle it.
+ */
+ BUG_ON(offset >= iomap->offset + iomap->length);
+
+ switch (iomap->type) {
+ case IOMAP_HOLE:
+ /*
+ * If the buffer is not up to date or beyond the current EOF,
+ * we need to mark it as new to ensure sub-block zeroing is
+ * executed if necessary.
+ */
+ if (!buffer_uptodate(bh) ||
+ (offset >= i_size_read(inode)))
+ set_buffer_new(bh);
+ break;
+ case IOMAP_DELALLOC:
+ if (!buffer_uptodate(bh) ||
+ (offset >= i_size_read(inode)))
+ set_buffer_new(bh);
+ set_buffer_uptodate(bh);
+ set_buffer_mapped(bh);
+ set_buffer_delay(bh);
+ break;
+ case IOMAP_UNWRITTEN:
+ /*
+ * For unwritten regions, we always need to ensure that
+ * sub-block writes cause the regions in the block we are not
+ * writing to are zeroed. Set the buffer as new to ensure this.
+ */
+ set_buffer_new(bh);
+ set_buffer_unwritten(bh);
+ /* FALLTHRU */
+ case IOMAP_MAPPED:
+ if (offset >= i_size_read(inode))
+ set_buffer_new(bh);
+ bh->b_blocknr = (iomap->blkno >> (inode->i_blkbits - 9)) +
+ ((offset - iomap->offset) >> inode->i_blkbits);
+ set_buffer_mapped(bh);
+ break;
+ }
+}
+
+int __block_write_begin_int(struct page *page, loff_t pos, unsigned len,
+ get_block_t *get_block, struct iomap *iomap)
{
unsigned from = pos & (PAGE_SIZE - 1);
unsigned to = from + len;
@@ -1928,9 +1983,14 @@
clear_buffer_new(bh);
if (!buffer_mapped(bh)) {
WARN_ON(bh->b_size != blocksize);
- err = get_block(inode, block, bh, 1);
- if (err)
- break;
+ if (get_block) {
+ err = get_block(inode, block, bh, 1);
+ if (err)
+ break;
+ } else {
+ iomap_to_bh(inode, block, bh, iomap);
+ }
+
if (buffer_new(bh)) {
unmap_underlying_metadata(bh->b_bdev,
bh->b_blocknr);
@@ -1971,6 +2031,12 @@
page_zero_new_buffers(page, from, to);
return err;
}
+
+int __block_write_begin(struct page *page, loff_t pos, unsigned len,
+ get_block_t *get_block)
+{
+ return __block_write_begin_int(page, pos, len, get_block, NULL);
+}
EXPORT_SYMBOL(__block_write_begin);
static int __block_commit_write(struct inode *inode, struct page *page,