struct inode *inode = page->mapping->host;
const unsigned blkbits = inode->i_blkbits;
const unsigned blocksize = 1 << blkbits;
- struct buffer_head map_bh;
- struct buffer_head *read_bh[MAX_BUF_PER_PAGE];
+ struct buffer_head *head, *bh;
unsigned block_in_page;
- unsigned block_start;
+ unsigned block_start, block_end;
sector_t block_in_file;
char *kaddr;
int nr_reads = 0;
- int i;
int ret = 0;
int is_mapped_to_disk = 1;
+ if (page_has_buffers(page))
+ return block_prepare_write(page, from, to, get_block);
+
if (PageMappedToDisk(page))
return 0;
+ /*
+ * Allocate buffers so that we can keep track of state, and potentially
+ * attach them to the page if an error occurs. In the common case of
+ * no error, they will just be freed again without ever being attached
+ * to the page (which is all OK, because we're under the page lock).
+ *
+ * Be careful: the buffer linked list is a NULL terminated one, rather
+ * than the circular one we're used to.
+ */
+ head = alloc_page_buffers(page, blocksize, 0);
+ if (!head)
+ return -ENOMEM;
+
block_in_file = (sector_t)page->index << (PAGE_CACHE_SHIFT - blkbits);
- map_bh.b_page = page;
/*
* We loop across all blocks in the page, whether or not they are
* part of the affected region. This is so we can discover if the
* page is fully mapped-to-disk.
*/
- for (block_start = 0, block_in_page = 0;
+ for (block_start = 0, block_in_page = 0, bh = head;
block_start < PAGE_CACHE_SIZE;
- block_in_page++, block_start += blocksize) {
- unsigned block_end = block_start + blocksize;
+ block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
int create;
- map_bh.b_state = 0;
+ block_end = block_start + blocksize;
+ bh->b_state = 0;
create = 1;
if (block_start >= to)
create = 0;
- map_bh.b_size = blocksize;
ret = get_block(inode, block_in_file + block_in_page,
- &map_bh, create);
+ bh, create);
if (ret)
goto failed;
- if (!buffer_mapped(&map_bh))
+ if (!buffer_mapped(bh))
is_mapped_to_disk = 0;
- if (buffer_new(&map_bh))
- unmap_underlying_metadata(map_bh.b_bdev,
- map_bh.b_blocknr);
- if (PageUptodate(page))
+ if (buffer_new(bh))
+ unmap_underlying_metadata(bh->b_bdev, bh->b_blocknr);
+ if (PageUptodate(page)) {
+ set_buffer_uptodate(bh);
continue;
- if (buffer_new(&map_bh) || !buffer_mapped(&map_bh)) {
+ }
+ if (buffer_new(bh) || !buffer_mapped(bh)) {
kaddr = kmap_atomic(page, KM_USER0);
if (block_start < from)
memset(kaddr+block_start, 0, from-block_start);
kunmap_atomic(kaddr, KM_USER0);
continue;
}
- if (buffer_uptodate(&map_bh))
+ if (buffer_uptodate(bh))
continue; /* reiserfs does this */
if (block_start < from || block_end > to) {
- struct buffer_head *bh = alloc_buffer_head(GFP_NOFS);
-
- if (!bh) {
- ret = -ENOMEM;
- goto failed;
- }
- bh->b_state = map_bh.b_state;
- atomic_set(&bh->b_count, 0);
- bh->b_this_page = NULL;
- bh->b_page = page;
- bh->b_blocknr = map_bh.b_blocknr;
- bh->b_size = blocksize;
- bh->b_data = (char *)(long)block_start;
- bh->b_bdev = map_bh.b_bdev;
- bh->b_private = NULL;
- read_bh[nr_reads++] = bh;
+ lock_buffer(bh);
+ bh->b_end_io = end_buffer_read_nobh;
+ submit_bh(READ, bh);
+ nr_reads++;
}
}
if (nr_reads) {
- struct buffer_head *bh;
-
/*
* The page is locked, so these buffers are protected from
* any VM or truncate activity. Hence we don't need to care
* for the buffer_head refcounts.
*/
- for (i = 0; i < nr_reads; i++) {
- bh = read_bh[i];
- lock_buffer(bh);
- bh->b_end_io = end_buffer_read_nobh;
- submit_bh(READ, bh);
- }
- for (i = 0; i < nr_reads; i++) {
- bh = read_bh[i];
+ for (bh = head; bh; bh = bh->b_this_page) {
wait_on_buffer(bh);
if (!buffer_uptodate(bh))
ret = -EIO;
- free_buffer_head(bh);
- read_bh[i] = NULL;
}
if (ret)
goto failed;
if (is_mapped_to_disk)
SetPageMappedToDisk(page);
+ do {
+ bh = head;
+ head = head->b_this_page;
+ free_buffer_head(bh);
+ } while (head);
+
return 0;
failed:
- for (i = 0; i < nr_reads; i++) {
- if (read_bh[i])
- free_buffer_head(read_bh[i]);
- }
-
/*
- * Error recovery is pretty slack. Clear the page and mark it dirty
- * so we'll later zero out any blocks which _were_ allocated.
+ * Error recovery is a bit difficult. We need to zero out blocks that
+ * were newly allocated, and dirty them to ensure they get written out.
+ * Buffers need to be attached to the page at this point, otherwise
+ * the handling of potential IO errors during writeout would be hard
+ * (could try doing synchronous writeout, but what if that fails too?)
*/
- zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
- SetPageUptodate(page);
- set_page_dirty(page);
+ spin_lock(&page->mapping->private_lock);
+ bh = head;
+ block_start = 0;
+ do {
+ if (PageUptodate(page))
+ set_buffer_uptodate(bh);
+ if (PageDirty(page))
+ set_buffer_dirty(bh);
+
+ block_end = block_start+blocksize;
+ if (block_end <= from)
+ goto next;
+ if (block_start >= to)
+ goto next;
+
+ if (buffer_new(bh)) {
+ clear_buffer_new(bh);
+ if (!buffer_uptodate(bh)) {
+ zero_user_page(page, block_start, bh->b_size, KM_USER0);
+ set_buffer_uptodate(bh);
+ }
+ mark_buffer_dirty(bh);
+ }
+next:
+ block_start = block_end;
+ if (!bh->b_this_page)
+ bh->b_this_page = head;
+ bh = bh->b_this_page;
+ } while (bh != head);
+ attach_page_buffers(page, head);
+ spin_unlock(&page->mapping->private_lock);
+
return ret;
}
EXPORT_SYMBOL(nobh_prepare_write);
struct inode *inode = page->mapping->host;
loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
+ if (page_has_buffers(page))
+ return generic_commit_write(file, page, from, to);
+
SetPageUptodate(page);
set_page_dirty(page);
if (pos > inode->i_size) {
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