projects/linux·commit afddba49

fs: introduce write_begin, write_end, and perform_write aops

afddba49 · Nick Piggin <[email protected]> · 2007-10-16 01:25:01 -07:00

These are intended to replace prepare_write and commit_write with more
flexible alternatives that are also able to avoid the buffered write
deadlock problems efficiently (which prepare_write is unable to do).

[[email protected]: API design contributions, code review and fixes]
[[email protected]: various fixes]
[[email protected]: new aop block_write_begin fix]
Signed-off-by: Nick Piggin <[email protected]>
Signed-off-by: Mark Fasheh <[email protected]>
Signed-off-by: Dmitriy Monakhov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Commit
afddba49d18f346e5cc2938b6ed7c512db18ca68
Parents
637aff46

Changes

11 files changed · +575 −206

FileStatusAddDelContent
Documentation/filesystems/Lockingmodified+6−3View file
Documentation/filesystems/vfs.txtmodified+45−0View file
drivers/block/loop.cmodified+29−46View file
fs/buffer.cmodified+169−32View file
fs/libfs.cmodified+44−0View file
fs/namei.cmodified+11−35View file
fs/splice.cmodified+7−62View file
include/linux/buffer_head.hmodified+10−0View file
include/linux/fs.hmodified+29−1View file
include/linux/pagemap.hmodified+2−0View file
mm/filemap.cmodified+223−27View file

Only the first 600 diff lines are shown. Download the complete patch.

Documentation/filesystems/Locking

View file
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index f0f8258..fe26cc9 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -178,15 +178,18 @@ prototypes:
locking rules:
All except set_page_dirty may block
- BKL PageLocked(page)
+ BKL PageLocked(page) i_sem
writepage: no yes, unlocks (see below)
readpage: no yes, unlocks
sync_page: no maybe
writepages: no
set_page_dirty no no
readpages: no
-prepare_write: no yes
-commit_write: no yes
+prepare_write: no yes yes
+commit_write: no yes yes
+write_begin: no locks the page yes
+write_end: no yes, unlocks yes
+perform_write: no n/a yes
bmap: yes
invalidatepage: no yes
releasepage: no yes

Documentation/filesystems/vfs.txt

View file
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index 045f3e0..281c19f 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -537,6 +537,12 @@ struct address_space_operations {
struct list_head *pages, unsigned nr_pages);
int (*prepare_write)(struct file *, struct page *, unsigned, unsigned);
int (*commit_write)(struct file *, struct page *, unsigned, unsigned);
+ int (*write_begin)(struct file *, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned flags,
+ struct page **pagep, void **fsdata);
+ int (*write_end)(struct file *, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata);
sector_t (*bmap)(struct address_space *, sector_t);
int (*invalidatepage) (struct page *, unsigned long);
int (*releasepage) (struct page *, int);
@@ -633,6 +639,45 @@ struct address_space_operations {
operations. It should avoid returning an error if possible -
errors should have been handled by prepare_write.
+ write_begin: This is intended as a replacement for prepare_write. The
+ key differences being that:
+ - it returns a locked page (in *pagep) rather than being
+ given a pre locked page;
+ - it must be able to cope with short writes (where the
+ length passed to write_begin is greater than the number
+ of bytes copied into the page).
+
+ Called by the generic buffered write code to ask the filesystem to
+ prepare to write len bytes at the given offset in the file. The
+ address_space should check that the write will be able to complete,
+ by allocating space if necessary and doing any other internal
+ housekeeping. If the write will update parts of any basic-blocks on
+ storage, then those blocks should be pre-read (if they haven't been
+ read already) so that the updated blocks can be written out properly.
+
+ The filesystem must return the locked pagecache page for the specified
+ offset, in *pagep, for the caller to write into.
+
+ flags is a field for AOP_FLAG_xxx flags, described in
+ include/linux/fs.h.
+
+ A void * may be returned in fsdata, which then gets passed into
+ write_end.
+
+ Returns 0 on success; < 0 on failure (which is the error code), in
+ which case write_end is not called.
+
+ write_end: After a successful write_begin, and data copy, write_end must
+ be called. len is the original len passed to write_begin, and copied
+ is the amount that was able to be copied (copied == len is always true
+ if write_begin was called with the AOP_FLAG_UNINTERRUPTIBLE flag).
+
+ The filesystem must take care of unlocking the page and releasing it
+ refcount, and updating i_size.
+
+ Returns < 0 on failure, otherwise the number of bytes (<= 'copied')
+ that were able to be copied into pagecache.
+
bmap: called by the VFS to map a logical block offset within object to
physical block number. This method is used by the FIBMAP
ioctl and for working with swap-files. To be able to swap to

drivers/block/loop.c

View file
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index b9233a0..a5f993a 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -204,14 +204,13 @@ lo_do_transfer(struct loop_device *lo, int cmd,
* do_lo_send_aops - helper for writing data to a loop device
*
* This is the fast version for backing filesystems which implement the address
- * space operations prepare_write and commit_write.
+ * space operations write_begin and write_end.
*/
static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
- int bsize, loff_t pos, struct page *page)
+ int bsize, loff_t pos, struct page *unused)
{
struct file *file = lo->lo_backing_file; /* kudos to NFsckingS */
struct address_space *mapping = file->f_mapping;
- const struct address_space_operations *aops = mapping->a_ops;
pgoff_t index;
unsigned offset, bv_offs;
int len, ret;
@@ -223,63 +222,47 @@ static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
len = bvec->bv_len;
while (len > 0) {
sector_t IV;
- unsigned size;
+ unsigned size, copied;
int transfer_result;
+ struct page *page;
+ void *fsdata;
IV = ((sector_t)index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);
size = PAGE_CACHE_SIZE - offset;
if (size > len)
size = len;
- page = grab_cache_page(mapping, index);
- if (unlikely(!page))
+
+ ret = pagecache_write_begin(file, mapping, pos, size, 0,
+ &page, &fsdata);
+ if (ret)
goto fail;
- ret = aops->prepare_write(file, page, offset,
- offset + size);
- if (unlikely(ret)) {
- if (ret == AOP_TRUNCATED_PAGE) {
- page_cache_release(page);
- continue;
- }
- goto unlock;
- }
+
transfer_result = lo_do_transfer(lo, WRITE, page, offset,
bvec->bv_page, bv_offs, size, IV);
- if (unlikely(transfer_result)) {
- /*
- * The transfer failed, but we still write the data to
- * keep prepare/commit calls balanced.
- */
- printk(KERN_ERR "loop: transfer error block %llu\n",
- (unsigned long long)index);
- zero_user_page(page, offset, size, KM_USER0);
- }
- flush_dcache_page(page);
- ret = aops->commit_write(file, page, offset,
- offset + size);
- if (unlikely(ret)) {
- if (ret == AOP_TRUNCATED_PAGE) {
- page_cache_release(page);
- continue;
- }
- goto unlock;
- }
+ copied = size;
if (unlikely(transfer_result))
- goto unlock;
- bv_offs += size;
- len -= size;
+ copied = 0;
+
+ ret = pagecache_write_end(file, mapping, pos, size, copied,
+ page, fsdata);
+ if (ret < 0)
+ goto fail;
+ if (ret < copied)
+ copied = ret;
+
+ if (unlikely(transfer_result))
+ goto fail;
+
+ bv_offs += copied;
+ len -= copied;
offset = 0;
index++;
- pos += size;
- unlock_page(page);
- page_cache_release(page);
+ pos += copied;
}
ret = 0;
out:
mutex_unlock(&mapping->host->i_mutex);
return ret;
-unlock:
- unlock_page(page);
- page_cache_release(page);
fail:
ret = -1;
goto out;
@@ -313,7 +296,7 @@ static int __do_lo_send_write(struct file *file,
* do_lo_send_direct_write - helper for writing data to a loop device
*
* This is the fast, non-transforming version for backing filesystems which do
- * not implement the address space operations prepare_write and commit_write.
+ * not implement the address space operations write_begin and write_end.
* It uses the write file operation which should be present on all writeable
* filesystems.
*/
@@ -332,7 +315,7 @@ static int do_lo_send_direct_write(struct loop_device *lo,
* do_lo_send_write - helper for writing data to a loop device
*
* This is the slow, transforming version for filesystems which do not
- * implement the address space operations prepare_write and commit_write. It
+ * implement the address space operations write_begin and write_end. It
* uses the write file operation which should be present on all writeable
* filesystems.
*
@@ -780,7 +763,7 @@ static int loop_set_fd(struct loop_device *lo, struct file *lo_file,
*/
if (!file->f_op->splice_read)
goto out_putf;
- if (aops->prepare_write && aops->commit_write)
+ if (aops->prepare_write || aops->write_begin)
lo_flags |= LO_FLAGS_USE_AOPS;
if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)
lo_flags |= LO_FLAGS_READ_ONLY;

fs/buffer.c

View file
diff --git a/fs/buffer.c b/fs/buffer.c
index 9ece6c2..68b8fbd 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1770,6 +1770,48 @@ recover:
goto done;
}
+/*
+ * If a page has any new buffers, zero them out here, and mark them uptodate
+ * and dirty so they'll be written out (in order to prevent uninitialised
+ * block data from leaking). And clear the new bit.
+ */
+void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
+{
+ unsigned int block_start, block_end;
+ struct buffer_head *head, *bh;
+
+ BUG_ON(!PageLocked(page));
+ if (!page_has_buffers(page))
+ return;
+
+ bh = head = page_buffers(page);
+ block_start = 0;
+ do {
+ block_end = block_start + bh->b_size;
+
+ if (buffer_new(bh)) {
+ if (block_end > from && block_start < to) {
+ if (!PageUptodate(page)) {
+ unsigned start, size;
+
+ start = max(from, block_start);
+ size = min(to, block_end) - start;
+
+ zero_user_page(page, start, size, KM_USER0);
+ set_buffer_uptodate(bh);
+ }
+
+ clear_buffer_new(bh);
+ mark_buffer_dirty(bh);
+ }
+ }
+
+ block_start = block_end;
+ bh = bh->b_this_page;
+ } while (bh != head);
+}
+EXPORT_SYMBOL(page_zero_new_buffers);
+
static int __block_prepare_write(struct inode *inode, struct page *page,
unsigned from, unsigned to, get_block_t *get_block)
{
@@ -1854,38 +1896,8 @@ static int __block_prepare_write(struct inode *inode, struct page *page,
if (!buffer_uptodate(*wait_bh))
err = -EIO;
}
- if (!err) {
- bh = head;
- do {
- if (buffer_new(bh))
- clear_buffer_new(bh);
- } while ((bh = bh->b_this_page) != head);
- return 0;
- }
- /* Error case: */
- /*
- * Zero out any newly allocated blocks to avoid exposing stale
- * data. If BH_New is set, we know that the block was newly
- * allocated in the above loop.
- */
- bh = head;
- block_start = 0;
- do {
- block_end = block_start+blocksize;
- if (block_end <= from)
- goto next_bh;
- if (block_start >= to)
- break;
- if (buffer_new(bh)) {
- clear_buffer_new(bh);
- zero_user_page(page, block_start, bh->b_size, KM_USER0);
- set_buffer_uptodate(bh);
- mark_buffer_dirty(bh);
- }
-next_bh:
- block_start = block_end;
- bh = bh->b_this_page;
- } while (bh != head);
+ if (unlikely(err))
+ page_zero_new_buffers(page, from, to);
return err;
}
@@ -1910,6 +1922,7 @@ static int __block_commit_write(struct inode *inode, struct page *page,
set_buffer_uptodate(bh);
mark_buffer_dirty(bh);
}
+ clear_buffer_new(bh);
}
/*
@@ -1924,6 +1937,130 @@ static int __block_commit_write(struct inode *inode, struct page *page,
}
/*
+ * block_write_begin takes care of the basic task of block allocation and
+ * bringing partial write blocks uptodate first.
+ *
+ * If *pagep is not NULL, then block_write_begin uses the locked page
+ * at *pagep rather than allocating its own. In this case, the page will
+ * not be unlocked or deallocated on failure.
+ */
+int block_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned flags,
+ struct page **pagep, void **fsdata,
+ get_block_t *get_block)
+{
+ struct inode *inode = mapping->host;
+ int status = 0;
+ struct page *page;
+ pgoff_t index;
+ unsigned start, end;
+ int ownpage = 0;
+
+ index = pos >> PAGE_CACHE_SHIFT;
+ start = pos & (PAGE_CACHE_SIZE - 1);
+ end = start + len;
+
+ page = *pagep;
+ if (page == NULL) {
+ ownpage = 1;
+ page = __grab_cache_page(mapping, index);
+ if (!page) {
+ status = -ENOMEM;
+ goto out;
+ }
+ *pagep = page;
+ } else
+ BUG_ON(!PageLocked(page));
+
+ status = __block_prepare_write(inode, page, start, end, get_block);
+ if (unlikely(status)) {
+ ClearPageUptodate(page);
+
+ if (ownpage) {
+ unlock_page(page);
+ page_cache_release(page);
+ *pagep = NULL;
+
+ /*
+ * prepare_write() may have instantiated a few blocks
+ * outside i_size. Trim these off again. Don't need
+ * i_size_read because we hold i_mutex.
+ */
+ if (pos + len > inode->i_size)
+ vmtruncate(inode, inode->i_size);
+ }
+ goto out;
+ }
+
+out:
+ return status;
+}
+EXPORT_SYMBOL(block_write_begin);
+
+int block_write_end(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata)
+{
+ struct inode *inode = mapping->host;
+ unsigned start;
+
+ start = pos & (PAGE_CACHE_SIZE - 1);
+
+ if (unlikely(copied < len)) {
+ /*
+ * The buffers that were written will now be uptodate, so we
+ * don't have to worry about a readpage reading them and
+ * overwriting a partial write. However if we have encountered
+ * a short write and only partially written into a buffer, it
+ * will not be marked uptodate, so a readpage might come in and
+ * destroy our partial write.
+ *
+ * Do the simplest thing, and just treat any short write to a
+ * non uptodate page as a zero-length write, and force the
+ * caller to redo the whole thing.
+ */
+ if (!PageUptodate(page))
+ copied = 0;
+
+ page_zero_new_buffers(page, start+copied, start+len);
+ }
+ flush_dcache_page(page);
+
+ /* This could be a short (even 0-length) commit */
+ __block_commit_write(inode, page, start, start+copied);
+
+ return copied;
+}
+EXPORT_SYMBOL(block_write_end);
+
+int generic_write_end(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata)
+{
+ struct inode *inode = mapping->host;
+
+ copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
+
+ /*
+ * No need to use i_size_read() here, the i_size
+ * cannot change under us because we hold i_mutex.
+ *
+ * But it's important to update i_size while still holding page lock:
+ * page writeout could otherwise come in and zero beyond i_size.
+ */
+ if (pos+copied > inode->i_size) {
+ i_size_write(inode, pos+copied);
+ mark_inode_dirty(inode);
+ }
+
+ unlock_page(page);
+ page_cache_release(page);
+
+ return copied;
+}
+EXPORT_SYMBOL(generic_write_end);
+
+/*
* Generic "read page" function for block devices that have the normal
* get_block functionality. This is most of the block device filesystems.
* Reads the page asynchronously --- the unlock_buffer() and

fs/libfs.c

View file
diff --git a/fs/libfs.c b/fs/libfs.c
index 5294de1..f2b32d3 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -351,6 +351,26 @@ int simple_prepare_write(struct file *file, struct page *page,
return 0;
}
+int simple_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned flags,
+ struct page **pagep, void **fsdata)
+{
+ struct page *page;
+ pgoff_t index;
+ unsigned from;
+
+ index = pos >> PAGE_CACHE_SHIFT;
+ from = pos & (PAGE_CACHE_SIZE - 1);
+
+ page = __grab_cache_page(mapping, index);
+ if (!page)
+ return -ENOMEM;
+
+ *pagep = page;
+
+ return simple_prepare_write(file, page, from, from+len);
+}
+
int simple_commit_write(struct file *file, struct page *page,
unsigned from, unsigned to)
{
@@ -369,6 +389,28 @@ int simple_commit_write(struct file *file, struct page *page,
return 0;
}
+int simple_write_end(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata)
+{
+ unsigned from = pos & (PAGE_CACHE_SIZE - 1);
+
+ /* zero the stale part of the page if we did a short copy */
+ if (copied < len) {
+ void *kaddr = kmap_atomic(page, KM_USER0);
+ memset(kaddr + from + copied, 0, len - copied);
+ flush_dcache_page(page);
+ kunmap_atomic(kaddr, KM_USER0);
+ }
+
+ simple_commit_write(file, page, from, from+copied);
+
+ unlock_page(page);
+ page_cache_release(page);
+
+ return copied;
+}
+
/*
* the inodes created here are not hashed. If you use iunique to generate
* unique inode values later for this filesystem, then you must take care
@@ -642,6 +684,8 @@ EXPORT_SYMBOL(dcache_dir_open);
EXPORT_SYMBOL(dcache_readdir);
EXPORT_SYMBOL(generic_read_dir);
EXPORT_SYMBOL(get_sb_pseudo);
+EXPORT_SYMBOL(simple_write_begin);
+EXPORT_SYMBOL(simple_write_end);
EXPORT_SYMBOL(simple_commit_write);
EXPORT_SYMBOL(simple_dir_inode_operations);
EXPORT_SYMBOL(simple_dir_operations);

fs/namei.c

View file
diff --git a/fs/namei.c b/fs/namei.c
index a83160a..b40b808 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2729,53 +2729,29 @@ int __page_symlink(struct inode *inode, const char *symname, int len,
{
struct address_space *mapping = inode->i_mapping;
struct page *page;
+ void *fsdata;
int err;
char *kaddr;
retry:
- err = -ENOMEM;
- page = find_or_create_page(mapping, 0, gfp_mask);
- if (!page)
- goto fail;
- err = mapping->a_ops->prepare_write(NULL, page, 0, len-1);
- if (err == AOP_TRUNCATED_PAGE) {
- page_cache_release(page);
- goto retry;
- }
+ err = pagecache_write_begin(NULL, mapping, 0, len-1,
+ AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
if (err)
- goto fail_map;
+ goto fail;
+
kaddr = kmap_atomic(page, KM_USER0);
memcpy(kaddr, symname, len-1);
kunmap_atomic(kaddr, KM_USER0);
- err = mapping->a_ops->commit_write(NULL, page, 0, len-1);
- if (err == AOP_TRUNCATED_PAGE) {
- page_cache_release(page);
- goto retry;
- }
- if (err)
- goto fail_map;
- /*
- * Notice that we are _not_ going to block here - end of page is
- * unmapped, so this will only try to map the rest of page, see
- * that it is unmapped (typically even will not look into inode -
- * ->i_size will be enough for everything) and zero it out.
- * OTOH it's obviously correct and should make the page up-to-date.
- */
- if (!PageUptodate(page)) {
- err = mapping->a_ops->readpage(NULL, page);
- if (err != AOP_TRUNCATED_PAGE)
- wait_on_page_locked(page);
- } else {
- unlock_page(page);
- }
- page_cache_release(page);
+
+ err = pagecache_write_end(NULL, mapping, 0, len-1, len-1,
+ page, fsdata);
if (err < 0)
goto fail;
+ if (err < len-1)
+ goto retry;
+
mark_inode_dirty(inode);
return 0;
-fail_map:
- unlock_page(page);
- page_cache_release(page);
fail:
return err;
}

fs/splice.c

View file
diff --git a/fs/splice.c b/fs/splice.c
index 2df6be4..a7568bc 100644
--- a/fs/splice.c
+++ b/fs/splice.c

This diff is incomplete. Download the complete patch.

include/linux/buffer_head.h

View file

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include/linux/fs.h

View file

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include/linux/pagemap.h

View file

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mm/filemap.c

View file

This diff is incomplete. Download the complete patch.