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ext4: simplify ext4_writepage()

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The actual code in ext4_writepage() is unnecessarily convoluted.
Simplify it so it is easier to understand, but otherwise logically
equivalent.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o 2010-10-27 21:30:09 -04:00
parent 5a87b7a5da
commit a42afc5f56
1 changed files with 25 additions and 48 deletions
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73
fs/ext4/inode.c
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@ -2704,7 +2704,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
static int ext4_writepage(struct page *page,
struct writeback_control *wbc)
{
int ret = 0;
int ret = 0, commit_write = 0;
loff_t size;
unsigned int len;
struct buffer_head *page_bufs = NULL;
@ -2717,60 +2717,37 @@ static int ext4_writepage(struct page *page,
else
len = PAGE_CACHE_SIZE;
if (page_has_buffers(page)) {
page_bufs = page_buffers(page);
if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
ext4_bh_delay_or_unwritten)) {
/*
* We don't want to do block allocation
* So redirty the page and return
* We may reach here when we do a journal commit
* via journal_submit_inode_data_buffers.
* If we don't have mapping block we just ignore
* them. We can also reach here via shrink_page_list
*/
/*
* If the page does not have buffers (for whatever reason),
* try to create them using block_prepare_write. If this
* fails, redirty the page and move on.
*/
if (!page_buffers(page)) {
if (block_prepare_write(page, 0, len,
noalloc_get_block_write)) {
redirty_page:
redirty_page_for_writepage(wbc, page);
unlock_page(page);
return 0;
}
} else {
commit_write = 1;
}
page_bufs = page_buffers(page);
if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
ext4_bh_delay_or_unwritten)) {
/*
* The test for page_has_buffers() is subtle:
* We know the page is dirty but it lost buffers. That means
* that at some moment in time after write_begin()/write_end()
* has been called all buffers have been clean and thus they
* must have been written at least once. So they are all
* mapped and we can happily proceed with mapping them
* and writing the page.
*
* Try to initialize the buffer_heads and check whether
* all are mapped and non delay. We don't want to
* do block allocation here.
* We don't want to do block allocation So redirty the
* page and return We may reach here when we do a
* journal commit via
* journal_submit_inode_data_buffers. If we don't
* have mapping block we just ignore them. We can also
* reach here via shrink_page_list
*/
ret = block_prepare_write(page, 0, len,
noalloc_get_block_write);
if (!ret) {
page_bufs = page_buffers(page);
/* check whether all are mapped and non delay */
if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
ext4_bh_delay_or_unwritten)) {
redirty_page_for_writepage(wbc, page);
unlock_page(page);
return 0;
}
} else {
/*
* We can't do block allocation here
* so just redity the page and unlock
* and return
*/
redirty_page_for_writepage(wbc, page);
unlock_page(page);
return 0;
}
goto redirty_page;
}
if (commit_write)
/* now mark the buffer_heads as dirty and uptodate */
block_commit_write(page, 0, len);
}
if (PageChecked(page) && ext4_should_journal_data(inode)) {
/*
@ -2781,7 +2758,7 @@ static int ext4_writepage(struct page *page,
return __ext4_journalled_writepage(page, len);
}
if (page_bufs && buffer_uninit(page_bufs)) {
if (buffer_uninit(page_bufs)) {
ext4_set_bh_endio(page_bufs, inode);
ret = block_write_full_page_endio(page, noalloc_get_block_write,
wbc, ext4_end_io_buffer_write);