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Subject[patch 06/22] consolidate generic_writepages and mpage_writepages
From: Miklos Szeredi <mszeredi@suse.cz>

Changes:
o fix theoretical NULL pointer dereference in __mpage_writepage
o merge Andrew Morton's cleanups


Clean up code duplication between mpage_writepages() and
generic_writepages().

The new generic function, write_cache_pages() takes a function pointer
argument, which will be called for each page to be written.

Maybe cifs_writepages() too can use this infrastructure, but I'm not
touching that with a ten-foot pole.

The upcoming page writeback support in fuse will also want this.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
Index: linux/fs/mpage.c
===================================================================
--- linux.orig/fs/mpage.c 2007-02-27 14:41:06.000000000 +0100
+++ linux/fs/mpage.c 2007-02-27 14:41:08.000000000 +0100
@@ -456,11 +456,18 @@ EXPORT_SYMBOL(mpage_readpage);
* written, so it can intelligently allocate a suitably-sized BIO. For now,
* just allocate full-size (16-page) BIOs.
*/
-static struct bio *
-__mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
- sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
- writepage_t writepage_fn)
+struct mpage_data {
+ struct bio *bio;
+ sector_t last_block_in_bio;
+ get_block_t *get_block;
+ unsigned use_writepage;
+};
+
+static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+ void *data)
{
+ struct mpage_data *mpd = data;
+ struct bio *bio = mpd->bio;
struct address_space *mapping = page->mapping;
struct inode *inode = page->mapping->host;
const unsigned blkbits = inode->i_blkbits;
@@ -478,6 +485,7 @@ __mpage_writepage(struct bio *bio, struc
int length;
struct buffer_head map_bh;
loff_t i_size = i_size_read(inode);
+ int ret = 0;

if (page_has_buffers(page)) {
struct buffer_head *head = page_buffers(page);
@@ -540,7 +548,7 @@ __mpage_writepage(struct bio *bio, struc

map_bh.b_state = 0;
map_bh.b_size = 1 << blkbits;
- if (get_block(inode, block_in_file, &map_bh, 1))
+ if (mpd->get_block(inode, block_in_file, &map_bh, 1))
goto confused;
if (buffer_new(&map_bh))
unmap_underlying_metadata(map_bh.b_bdev,
@@ -589,7 +597,7 @@ page_is_mapped:
/*
* This page will go to BIO. Do we need to send this BIO off first?
*/
- if (bio && *last_block_in_bio != blocks[0] - 1)
+ if (bio && mpd->last_block_in_bio != blocks[0] - 1)
bio = mpage_bio_submit(WRITE, bio);

alloc_new:
@@ -646,7 +654,7 @@ alloc_new:
boundary_block, 1 << blkbits);
}
} else {
- *last_block_in_bio = blocks[blocks_per_page - 1];
+ mpd->last_block_in_bio = blocks[blocks_per_page - 1];
}
goto out;

@@ -654,18 +662,19 @@ confused:
if (bio)
bio = mpage_bio_submit(WRITE, bio);

- if (writepage_fn) {
- *ret = (*writepage_fn)(page, wbc);
+ if (mpd->use_writepage && mapping->a_ops->writepage) {
+ ret = mapping->a_ops->writepage(page, wbc);
} else {
- *ret = -EAGAIN;
+ ret = -EAGAIN;
goto out;
}
/*
* The caller has a ref on the inode, so *mapping is stable
*/
- mapping_set_error(mapping, *ret);
+ mapping_set_error(mapping, ret);
out:
- return bio;
+ mpd->bio = bio;
+ return ret;
}

/**
@@ -688,120 +697,27 @@ out:
* the call was made get new I/O started against them. If wbc->sync_mode is
* WB_SYNC_ALL then we were called for data integrity and we must wait for
* existing IO to complete.
- *
- * If you fix this you should check generic_writepages() also!
*/
int
mpage_writepages(struct address_space *mapping,
struct writeback_control *wbc, get_block_t get_block)
{
- struct backing_dev_info *bdi = mapping->backing_dev_info;
- struct bio *bio = NULL;
- sector_t last_block_in_bio = 0;
- int ret = 0;
- int done = 0;
- int (*writepage)(struct page *page, struct writeback_control *wbc);
- struct pagevec pvec;
- int nr_pages;
- pgoff_t index;
- pgoff_t end; /* Inclusive */
- int scanned = 0;
- int range_whole = 0;
-
- if (wbc->nonblocking && bdi_write_congested(bdi)) {
- wbc->encountered_congestion = 1;
- return 0;
- }
+ int ret;

- writepage = NULL;
- if (get_block == NULL)
- writepage = mapping->a_ops->writepage;
-
- pagevec_init(&pvec, 0);
- if (wbc->range_cyclic) {
- index = mapping->writeback_index; /* Start from prev offset */
- end = -1;
- } else {
- index = wbc->range_start >> PAGE_CACHE_SHIFT;
- end = wbc->range_end >> PAGE_CACHE_SHIFT;
- if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
- range_whole = 1;
- scanned = 1;
+ if (!get_block)
+ ret = generic_writepages(mapping, wbc);
+ else {
+ struct mpage_data mpd = {
+ .bio = NULL,
+ .last_block_in_bio = 0,
+ .get_block = get_block,
+ .use_writepage = 1,
+ };
+
+ ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
+ if (mpd.bio)
+ mpage_bio_submit(WRITE, mpd.bio);
}
-retry:
- while (!done && (index <= end) &&
- (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
- PAGECACHE_TAG_DIRTY,
- min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
- unsigned i;
-
- scanned = 1;
- for (i = 0; i < nr_pages; i++) {
- struct page *page = pvec.pages[i];
-
- /*
- * At this point we hold neither mapping->tree_lock nor
- * lock on the page itself: the page may be truncated or
- * invalidated (changing page->mapping to NULL), or even
- * swizzled back from swapper_space to tmpfs file
- * mapping
- */
-
- lock_page(page);
-
- if (unlikely(page->mapping != mapping)) {
- unlock_page(page);
- continue;
- }
-
- if (!wbc->range_cyclic && page->index > end) {
- done = 1;
- unlock_page(page);
- continue;
- }
-
- if (wbc->sync_mode != WB_SYNC_NONE)
- wait_on_page_writeback(page);
-
- if (PageWriteback(page) ||
- !clear_page_dirty_for_io(page)) {
- unlock_page(page);
- continue;
- }
-
- if (writepage) {
- ret = (*writepage)(page, wbc);
- mapping_set_error(mapping, ret);
- } else {
- bio = __mpage_writepage(bio, page, get_block,
- &last_block_in_bio, &ret, wbc,
- page->mapping->a_ops->writepage);
- }
- if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
- unlock_page(page);
- if (ret || (--(wbc->nr_to_write) <= 0))
- done = 1;
- if (wbc->nonblocking && bdi_write_congested(bdi)) {
- wbc->encountered_congestion = 1;
- done = 1;
- }
- }
- pagevec_release(&pvec);
- cond_resched();
- }
- if (!scanned && !done) {
- /*
- * We hit the last page and there is more work to be done: wrap
- * back to the start of the file
- */
- scanned = 1;
- index = 0;
- goto retry;
- }
- if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
- mapping->writeback_index = index;
- if (bio)
- mpage_bio_submit(WRITE, bio);
return ret;
}
EXPORT_SYMBOL(mpage_writepages);
@@ -809,15 +725,15 @@ EXPORT_SYMBOL(mpage_writepages);
int mpage_writepage(struct page *page, get_block_t get_block,
struct writeback_control *wbc)
{
- int ret = 0;
- struct bio *bio;
- sector_t last_block_in_bio = 0;
-
- bio = __mpage_writepage(NULL, page, get_block,
- &last_block_in_bio, &ret, wbc, NULL);
- if (bio)
- mpage_bio_submit(WRITE, bio);
-
+ struct mpage_data mpd = {
+ .bio = NULL,
+ .last_block_in_bio = 0,
+ .get_block = get_block,
+ .use_writepage = 0,
+ };
+ int ret = __mpage_writepage(page, wbc, &mpd);
+ if (mpd.bio)
+ mpage_bio_submit(WRITE, mpd.bio);
return ret;
}
EXPORT_SYMBOL(mpage_writepage);
Index: linux/include/linux/mpage.h
===================================================================
--- linux.orig/include/linux/mpage.h 2007-02-27 14:40:55.000000000 +0100
+++ linux/include/linux/mpage.h 2007-02-27 14:41:08.000000000 +0100
@@ -12,7 +12,6 @@
#ifdef CONFIG_BLOCK

struct writeback_control;
-typedef int (writepage_t)(struct page *page, struct writeback_control *wbc);

int mpage_readpages(struct address_space *mapping, struct list_head *pages,
unsigned nr_pages, get_block_t get_block);
Index: linux/include/linux/writeback.h
===================================================================
--- linux.orig/include/linux/writeback.h 2007-02-27 14:41:07.000000000 +0100
+++ linux/include/linux/writeback.h 2007-02-27 14:41:08.000000000 +0100
@@ -109,9 +109,15 @@ balance_dirty_pages_ratelimited(struct a
balance_dirty_pages_ratelimited_nr(mapping, 1);
}

+typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
+ void *data);
+
int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0);
-extern int generic_writepages(struct address_space *mapping,
- struct writeback_control *wbc);
+int generic_writepages(struct address_space *mapping,
+ struct writeback_control *wbc);
+int write_cache_pages(struct address_space *mapping,
+ struct writeback_control *wbc, writepage_t writepage,
+ void *data);
int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
int sync_page_range(struct inode *inode, struct address_space *mapping,
loff_t pos, loff_t count);
Index: linux/mm/page-writeback.c
===================================================================
--- linux.orig/mm/page-writeback.c 2007-02-27 14:41:08.000000000 +0100
+++ linux/mm/page-writeback.c 2007-02-27 14:41:08.000000000 +0100
@@ -567,31 +567,27 @@ void __init page_writeback_init(void)
}

/**
- * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
+ * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
* @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ * @writepage: function called for each page
+ * @data: data passed to writepage function
*
- * This is a library function, which implements the writepages()
- * address_space_operation.
- *
- * If a page is already under I/O, generic_writepages() skips it, even
+ * If a page is already under I/O, write_cache_pages() skips it, even
* if it's dirty. This is desirable behaviour for memory-cleaning writeback,
* but it is INCORRECT for data-integrity system calls such as fsync(). fsync()
* and msync() need to guarantee that all the data which was dirty at the time
* the call was made get new I/O started against them. If wbc->sync_mode is
* WB_SYNC_ALL then we were called for data integrity and we must wait for
* existing IO to complete.
- *
- * Derived from mpage_writepages() - if you fix this you should check that
- * also!
*/
-int generic_writepages(struct address_space *mapping,
- struct writeback_control *wbc)
+int write_cache_pages(struct address_space *mapping,
+ struct writeback_control *wbc, writepage_t writepage,
+ void *data)
{
struct backing_dev_info *bdi = mapping->backing_dev_info;
int ret = 0;
int done = 0;
- int (*writepage)(struct page *page, struct writeback_control *wbc);
struct pagevec pvec;
int nr_pages;
pgoff_t index;
@@ -604,12 +600,6 @@ int generic_writepages(struct address_sp
return 0;
}

- writepage = mapping->a_ops->writepage;
-
- /* deal with chardevs and other special file */
- if (!writepage)
- return 0;
-
pagevec_init(&pvec, 0);
if (wbc->range_cyclic) {
index = mapping->writeback_index; /* Start from prev offset */
@@ -661,8 +651,7 @@ retry:
continue;
}

- ret = (*writepage)(page, wbc);
- mapping_set_error(mapping, ret);
+ ret = (*writepage)(page, wbc, data);

if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
unlock_page(page);
@@ -689,6 +678,38 @@ retry:
mapping->writeback_index = index;
return ret;
}
+EXPORT_SYMBOL(write_cache_pages);
+
+/*
+ * Function used by generic_writepages to call the real writepage
+ * function and set the mapping flags on error
+ */
+static int __writepage(struct page *page, struct writeback_control *wbc,
+ void *data)
+{
+ struct address_space *mapping = data;
+ int ret = mapping->a_ops->writepage(page, wbc);
+ mapping_set_error(mapping, ret);
+ return ret;
+}
+
+/**
+ * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
+ * @mapping: address space structure to write
+ * @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ *
+ * This is a library function, which implements the writepages()
+ * address_space_operation.
+ */
+int generic_writepages(struct address_space *mapping,
+ struct writeback_control *wbc)
+{
+ /* deal with chardevs and other special file */
+ if (!mapping->a_ops->writepage)
+ return 0;
+
+ return write_cache_pages(mapping, wbc, __writepage, mapping);
+}

EXPORT_SYMBOL(generic_writepages);

--
-
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