[patch 2/5] fs: introduce new aops and infrastructure

From: Nick Piggin
Date: Wed Mar 14 2007 - 09:39:01 EST

Introduce write_begin, write_end, and perform_write aops.

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).

Documentation/filesystems/Locking | 9 +
Documentation/filesystems/vfs.txt | 38 ++++++
drivers/block/loop.c | 69 ++++-------
fs/buffer.c | 144 ++++++++++++++++++++----
fs/libfs.c | 40 ++++++
fs/namei.c | 47 ++-----
fs/splice.c | 106 +----------------
include/linux/buffer_head.h | 7 +
include/linux/fs.h | 29 ++++
include/linux/pagemap.h | 2
mm/filemap.c | 228 ++++++++++++++++++++++++++++++++++----
11 files changed, 494 insertions(+), 225 deletions(-)

Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h
+++ linux-2.6/include/linux/fs.h
@@ -449,6 +449,17 @@ struct address_space_operations {
*/
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, int intr,
+ 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);
+
+ int (*perform_write)(struct file *, struct address_space *,
+ struct iov_iter *, loff_t);
+
/* Unfortunately this kludge is needed for FIBMAP. Don't use it */
sector_t (*bmap)(struct address_space *, sector_t);
void (*invalidatepage) (struct page *, unsigned long);
@@ -463,6 +474,18 @@ struct address_space_operations {
int (*launder_page) (struct page *);
};

+/*
+ * pagecache_write_begin/pagecache_write_end must be used by general code
+ * to write into the pagecache.
+ */
+int pagecache_write_begin(struct file *, struct address_space *mapping,
+ loff_t pos, unsigned len, int intr,
+ struct page **pagep, void **fsdata);
+
+int pagecache_write_end(struct file *, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata);
+
struct backing_dev_info;
struct address_space {
struct inode *host; /* owner: inode, block_device */
@@ -1902,6 +1925,12 @@ extern int simple_prepare_write(struct f
unsigned offset, unsigned to);
extern int simple_commit_write(struct file *file, struct page *page,
unsigned offset, unsigned to);
+extern int simple_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, int intr,
+ struct page **pagep, void **fsdata);
+extern int simple_write_end(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata);

extern struct dentry *simple_lookup(struct inode *, struct dentry *, struct nameidata *);
extern ssize_t generic_read_dir(struct file *, char __user *, size_t, loff_t *);
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -2049,6 +2049,88 @@ inline int generic_write_checks(struct f
}
EXPORT_SYMBOL(generic_write_checks);

+int pagecache_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, int intr,
+ struct page **pagep, void **fsdata)
+{
+ const struct address_space_operations *aops = mapping->a_ops;
+
+ if (aops->write_begin)
+ return aops->write_begin(file, mapping, pos, len, intr, pagep, fsdata);
+ else {
+ int ret;
+ pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+ unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
+ struct inode *inode = mapping->host;
+ struct page *page;
+again:
+ page = __grab_cache_page(mapping, index);
+ *pagep = page;
+ if (!page)
+ return -ENOMEM;
+
+ if (intr && !PageUptodate(page)) {
+ /*
+ * There is no way to resolve a short write situation
+ * for a !Uptodate page (except by double copying in
+ * the caller done by generic_perform_write_2copy).
+ *
+ * Instead, we have to bring it uptodate here.
+ */
+ ret = aops->readpage(file, page);
+ page_cache_release(page);
+ if (ret) {
+ if (ret == AOP_TRUNCATED_PAGE)
+ goto again;
+ return ret;
+ }
+ goto again;
+ }
+
+ ret = aops->prepare_write(file, page, offset, offset+len);
+ if (ret) {
+ if (ret != AOP_TRUNCATED_PAGE)
+ unlock_page(page);
+ page_cache_release(page);
+ if (pos + len > inode->i_size)
+ vmtruncate(inode, inode->i_size);
+ if (ret == AOP_TRUNCATED_PAGE)
+ goto again;
+ }
+ return ret;
+ }
+}
+EXPORT_SYMBOL(pagecache_write_begin);
+
+int pagecache_write_end(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata)
+{
+ const struct address_space_operations *aops = mapping->a_ops;
+ int ret;
+
+ if (aops->write_begin)
+ ret = aops->write_end(file, mapping, pos, len, copied, page, fsdata);
+ else {
+ int ret;
+ unsigned offset = pos & (PAGE_CACHE_SIZE - 1);
+ struct inode *inode = mapping->host;
+
+ flush_dcache_page(page);
+ ret = aops->commit_write(file, page, offset, offset+len);
+ if (ret < 0) {
+ unlock_page(page);
+ page_cache_release(page);
+ if (pos + len > inode->i_size)
+ vmtruncate(inode, inode->i_size);
+ } else
+ ret = copied;
+ }
+
+ return copied;
+}
+EXPORT_SYMBOL(pagecache_write_end);
+
ssize_t
generic_file_direct_write(struct kiocb *iocb, const struct iovec *iov,
unsigned long *nr_segs, loff_t pos, loff_t *ppos,
@@ -2092,8 +2174,7 @@ EXPORT_SYMBOL(generic_file_direct_write)
* Find or create a page at the given pagecache position. Return the locked
* page. This function is specifically for buffered writes.
*/
-static struct page *__grab_cache_page(struct address_space *mapping,
- pgoff_t index)
+struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index)
{
int status;
struct page *page;
@@ -2115,19 +2196,14 @@ repeat:
return page;
}

-ssize_t
-generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
- unsigned long nr_segs, loff_t pos, loff_t *ppos,
- size_t count, ssize_t written)
+static ssize_t generic_perform_write_2copy(struct file *file,
+ struct iov_iter *i, loff_t pos)
{
- struct file *file = iocb->ki_filp;
struct address_space *mapping = file->f_mapping;
const struct address_space_operations *a_ops = mapping->a_ops;
- struct inode *inode = mapping->host;
- long status = 0;
- struct iov_iter i;
-
- iov_iter_init(&i, iov, nr_segs, count, written);
+ struct inode *inode = mapping->host;
+ long status = 0;
+ ssize_t written = 0;

do {
struct page *src_page;
@@ -2140,7 +2216,7 @@ generic_file_buffered_write(struct kiocb
offset = (pos & (PAGE_CACHE_SIZE - 1));
index = pos >> PAGE_CACHE_SHIFT;
bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
- iov_iter_count(&i));
+ iov_iter_count(i));

/*
* a non-NULL src_page indicates that we're doing the
@@ -2158,7 +2234,7 @@ generic_file_buffered_write(struct kiocb
* to check that the address is actually valid, when atomic
* usercopies are used, below.
*/
- if (unlikely(iov_iter_fault_in_readable(&i))) {
+ if (unlikely(iov_iter_fault_in_readable(i))) {
status = -EFAULT;
break;
}
@@ -2189,7 +2265,7 @@ generic_file_buffered_write(struct kiocb
* same reason as we can't take a page fault with a
* page locked (as explained below).
*/
- copied = iov_iter_copy_from_user(src_page, &i,
+ copied = iov_iter_copy_from_user(src_page, i,
offset, bytes);
if (unlikely(copied == 0)) {
status = -EFAULT;
@@ -2228,7 +2304,7 @@ generic_file_buffered_write(struct kiocb
* really matter.
*/
pagefault_disable();
- copied = iov_iter_copy_from_user_atomic(page, &i,
+ copied = iov_iter_copy_from_user_atomic(page, i,
offset, bytes);
pagefault_enable();
} else {
@@ -2254,9 +2330,9 @@ generic_file_buffered_write(struct kiocb
if (src_page)
page_cache_release(src_page);

- iov_iter_advance(&i, copied);
- written += copied;
+ iov_iter_advance(i, copied);
pos += copied;
+ written += copied;

balance_dirty_pages_ratelimited(mapping);
cond_resched();
@@ -2280,13 +2356,119 @@ fs_write_aop_error:
continue;
else
break;
- } while (iov_iter_count(&i));
- *ppos = pos;
+ } while (iov_iter_count(i));
+
+ return written ? written : status;
+}
+
+static ssize_t generic_perform_write(struct file *file,
+ struct iov_iter *i, loff_t pos)
+{
+ struct address_space *mapping = file->f_mapping;
+ const struct address_space_operations *a_ops = mapping->a_ops;
+ long status = 0;
+ ssize_t written = 0;
+
+ do {
+ struct page *page;
+ pgoff_t index; /* Pagecache index for current page */
+ unsigned long offset; /* Offset into pagecache page */
+ unsigned long bytes; /* Bytes to write to page */
+ size_t copied; /* Bytes copied from user */
+ void *fsdata;
+
+ offset = (pos & (PAGE_CACHE_SIZE - 1));
+ index = pos >> PAGE_CACHE_SHIFT;
+ bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
+ iov_iter_count(i));
+
+again:
+
+ /*
+ * Bring in the user page that we will copy from _first_.
+ * Otherwise there's a nasty deadlock on copying from the
+ * same page as we're writing to, without it being marked
+ * up-to-date.
+ *
+ * Not only is this an optimisation, but it is also required
+ * to check that the address is actually valid, when atomic
+ * usercopies are used, below.
+ */
+ if (unlikely(iov_iter_fault_in_readable(i))) {
+ status = -EFAULT;
+ break;
+ }
+
+ status = a_ops->write_begin(file, mapping, pos, bytes, 1,
+ &page, &fsdata);
+ if (unlikely(status))
+ break;
+
+ pagefault_disable();
+ copied = iov_iter_copy_from_user_atomic(page, i, offset, bytes);
+ pagefault_enable();
+ flush_dcache_page(page);
+
+ status = a_ops->write_end(file, mapping, pos, bytes, copied,
+ page, fsdata);
+ if (unlikely(status < 0))
+ break;
+ copied = status;
+
+ cond_resched();
+
+ if (unlikely(copied == 0)) {
+ /*
+ * If we were unable to copy any data at all, we must
+ * fall back to a single segment length write.
+ *
+ * If we didn't fallback here, we could livelock
+ * because not all segments in the iov can be copied at
+ * once without a pagefault.
+ */
+ bytes = min_t(unsigned long, PAGE_CACHE_SIZE - offset,
+ iov_iter_single_seg_count(i));
+ goto again;
+ }
+ iov_iter_advance(i, copied);
+ pos += copied;
+ written += copied;
+
+ balance_dirty_pages_ratelimited(mapping);
+
+ } while (iov_iter_count(i));
+
+ return written ? written : status;
+}
+
+ssize_t
+generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
+ unsigned long nr_segs, loff_t pos, loff_t *ppos,
+ size_t count, ssize_t written)
+{
+ struct file *file = iocb->ki_filp;
+ struct address_space *mapping = file->f_mapping;
+ const struct address_space_operations *a_ops = mapping->a_ops;
+ struct inode *inode = mapping->host;
+ long status = 0;
+ struct iov_iter i;
+
+ iov_iter_init(&i, iov, nr_segs, count, written);
+ if (a_ops->perform_write)
+ status = a_ops->perform_write(file, mapping, &i, pos);
+ else if (a_ops->write_begin)
+ status = generic_perform_write(file, &i, pos);
+ else
+ status = generic_perform_write_2copy(file, &i, pos);

- /*
- * For now, when the user asks for O_SYNC, we'll actually give O_DSYNC
- */
if (likely(status >= 0)) {
+ written += status;
+ *ppos = pos + status;
+
+ /*
+ * For now, when the user asks for O_SYNC, we'll actually give
+ * O_DSYNC
+ */
if (unlikely((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
if (!a_ops->writepage || !is_sync_kiocb(iocb))
status = generic_osync_inode(inode, mapping,
Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -1846,36 +1846,50 @@ static int __block_prepare_write(struct
} 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;
+ page_zero_new_buffers(page, from, to);
+ return err;
+}
+
+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+blocksize;
- if (block_end <= from)
- goto next_bh;
- if (block_start >= to)
- break;
+ block_end = block_start + bh->b_size;
+
if (buffer_new(bh)) {
- void *kaddr;
+ if (block_end > from && block_start < to) {
+ if (!PageUptodate(page)) {
+ unsigned start, end;
+ void *kaddr;
+
+ start = max(from, block_start);
+ end = min(to, block_end);
+
+ kaddr = kmap_atomic(page, KM_USER0);
+ memset(kaddr+start, 0, block_end-end);
+ flush_dcache_page(page);
+ kunmap_atomic(kaddr, KM_USER0);
+ set_buffer_uptodate(bh);
+ }

- clear_buffer_new(bh);
- kaddr = kmap_atomic(page, KM_USER0);
- memset(kaddr+block_start, 0, bh->b_size);
- flush_dcache_page(page);
- kunmap_atomic(kaddr, KM_USER0);
- set_buffer_uptodate(bh);
- mark_buffer_dirty(bh);
+ clear_buffer_new(bh);
+ mark_buffer_dirty(bh);
+ }
}
-next_bh:
+
block_start = block_end;
bh = bh->b_this_page;
} while (bh != head);
- return err;
}

static int __block_commit_write(struct inode *inode, struct page *page,
@@ -1899,6 +1913,7 @@ static int __block_commit_write(struct i
set_buffer_uptodate(bh);
mark_buffer_dirty(bh);
}
+ clear_buffer_new(bh);
}

/*
@@ -1912,6 +1927,93 @@ static int __block_commit_write(struct i
return 0;
}

+int block_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, int intr,
+ 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;
+
+ index = pos >> PAGE_CACHE_SHIFT;
+ start = pos & (PAGE_CACHE_SIZE - 1);
+ end = start + len;
+
+ page = *pagep;
+ if (page == NULL) {
+ page = __grab_cache_page(mapping, index);
+ if (!page) {
+ status = -ENOMEM;
+ goto out;
+ }
+ *pagep = page;
+ }
+
+ status = __block_prepare_write(inode, page, start, end, get_block);
+ if (unlikely(status)) {
+ ClearPageUptodate(page);
+
+ unlock_page(page);
+ page_cache_release(page);
+
+ /*
+ * 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;
+}
+
+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))
+ 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);
+
+ /*
+ * The buffers that were written will now be uptodate, so we don't
+ * have to worry about a readpage reading them again.
+ * XXX: however I'm not sure about partial writes to buffers. Must
+ * recheck that, and hopefully we can remove the below test.
+ */
+ if (!PageUptodate(page))
+ copied = 0;
+
+ unlock_page(page);
+ mark_page_accessed(page); /* XXX: put this in caller? */
+ page_cache_release(page);
+
+ /*
+ * No need to use i_size_read() here, the i_size
+ * cannot change under us because we hold i_mutex.
+ */
+ if (pos+copied > inode->i_size) {
+ i_size_write(inode, pos+copied);
+ mark_inode_dirty(inode);
+ }
+
+ return copied;
+}
+
/*
* Generic "read page" function for block devices that have the normal
* get_block functionality. This is most of the block device filesystems.
Index: linux-2.6/include/linux/buffer_head.h
===================================================================
--- linux-2.6.orig/include/linux/buffer_head.h
+++ linux-2.6/include/linux/buffer_head.h
@@ -202,6 +202,13 @@ void block_invalidatepage(struct page *p
int block_write_full_page(struct page *page, get_block_t *get_block,
struct writeback_control *wbc);
int block_read_full_page(struct page*, get_block_t*);
+int block_write_begin(struct file *, struct address_space *,
+ loff_t, unsigned, int,
+ struct page **, void **, get_block_t*);
+int block_write_end(struct file *, struct address_space *,
+ loff_t, unsigned, unsigned,
+ struct page *, void *);
+void page_zero_new_buffers(struct page *page, unsigned from, unsigned to);
int block_prepare_write(struct page*, unsigned, unsigned, get_block_t*);
int cont_prepare_write(struct page*, unsigned, unsigned, get_block_t*,
loff_t *);
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h
+++ linux-2.6/include/linux/pagemap.h
@@ -85,6 +85,8 @@ unsigned find_get_pages_contig(struct ad
unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
int tag, unsigned int nr_pages, struct page **pages);

+struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index);
+
/*
* Returns locked page at given index in given cache, creating it if needed.
*/
Index: linux-2.6/fs/libfs.c
===================================================================
--- linux-2.6.orig/fs/libfs.c
+++ linux-2.6/fs/libfs.c
@@ -342,6 +342,24 @@ int simple_prepare_write(struct file *fi
return 0;
}

+int simple_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, int intr,
+ 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;
+
+ return simple_prepare_write(file, page, from, from+len);
+}
+
int simple_commit_write(struct file *file, struct page *page,
unsigned from, unsigned to)
{
@@ -360,6 +378,28 @@ int simple_commit_write(struct file *fil
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;
+}
+
int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files)
{
struct inode *inode;
Index: linux-2.6/drivers/block/loop.c
===================================================================
--- linux-2.6.orig/drivers/block/loop.c
+++ linux-2.6/drivers/block/loop.c
@@ -206,11 +206,10 @@ lo_do_transfer(struct loop_device *lo, i
* space operations prepare_write and commit_write.
*/
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;
@@ -222,67 +221,47 @@ static int do_lo_send_aops(struct loop_d
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, 1,
+ &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)) {
- char *kaddr;
+ copied = size;
+ if (unlikely(transfer_result))
+ copied = 0;
+
+ ret = pagecache_write_end(file, mapping, pos, size, copied,
+ page, fsdata);
+ if (ret < 0)
+ goto fail;
+ if (ret < copied)
+ copied = ret;

- /*
- * 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);
- kaddr = kmap_atomic(page, KM_USER0);
- memset(kaddr + offset, 0, size);
- kunmap_atomic(kaddr, 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;
- }
if (unlikely(transfer_result))
- goto unlock;
- bv_offs += size;
- len -= size;
+ 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;
Index: linux-2.6/fs/namei.c
===================================================================
--- linux-2.6.orig/fs/namei.c
+++ linux-2.6/fs/namei.c
@@ -2688,53 +2688,30 @@ int __page_symlink(struct inode *inode,
{
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, PAGE_CACHE_SIZE, 0,
+ &page, &fsdata);
if (err)
- goto fail_map;
+ goto fail;
+
kaddr = kmap_atomic(page, KM_USER0);
memcpy(kaddr, symname, len-1);
+ memset(kaddr+len-1, 0, PAGE_CACHE_SIZE-(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, PAGE_CACHE_SIZE, PAGE_CACHE_SIZE,
+ page, fsdata);
if (err < 0)
goto fail;
+ if (err < PAGE_CACHE_SIZE)
+ goto retry;
+
mark_inode_dirty(inode);
return 0;
-fail_map:
- unlock_page(page);
- page_cache_release(page);
fail:
return err;
}
Index: linux-2.6/fs/splice.c
===================================================================
--- linux-2.6.orig/fs/splice.c
+++ linux-2.6/fs/splice.c
@@ -559,7 +559,7 @@ static int pipe_to_file(struct pipe_inod
struct address_space *mapping = file->f_mapping;
unsigned int offset, this_len;
struct page *page;
- pgoff_t index;
+ void *fsdata;
int ret;

/*
@@ -569,13 +569,13 @@ static int pipe_to_file(struct pipe_inod
if (unlikely(ret))
return ret;

- index = sd->pos >> PAGE_CACHE_SHIFT;
offset = sd->pos & ~PAGE_CACHE_MASK;

this_len = sd->len;
if (this_len + offset > PAGE_CACHE_SIZE)
this_len = PAGE_CACHE_SIZE - offset;

+#if 0
/*
* Reuse buf page, if SPLICE_F_MOVE is set and we are doing a full
* page.
@@ -587,86 +587,11 @@ static int pipe_to_file(struct pipe_inod
* locked on successful return.
*/
if (buf->ops->steal(pipe, buf))
- goto find_page;
+#endif

- page = buf->page;
- if (add_to_page_cache(page, mapping, index, GFP_KERNEL)) {
- unlock_page(page);
- goto find_page;
- }
-
- page_cache_get(page);
-
- if (!(buf->flags & PIPE_BUF_FLAG_LRU))
- lru_cache_add(page);
- } else {
-find_page:
- page = find_lock_page(mapping, index);
- if (!page) {
- ret = -ENOMEM;
- page = page_cache_alloc_cold(mapping);
- if (unlikely(!page))
- goto out_ret;
-
- /*
- * This will also lock the page
- */
- ret = add_to_page_cache_lru(page, mapping, index,
- GFP_KERNEL);
- if (unlikely(ret))
- goto out;
- }
-
- /*
- * We get here with the page locked. If the page is also
- * uptodate, we don't need to do more. If it isn't, we
- * may need to bring it in if we are not going to overwrite
- * the full page.
- */
- if (!PageUptodate(page)) {
- if (this_len < PAGE_CACHE_SIZE) {
- ret = mapping->a_ops->readpage(file, page);
- if (unlikely(ret))
- goto out;
-
- lock_page(page);
-
- if (!PageUptodate(page)) {
- /*
- * Page got invalidated, repeat.
- */
- if (!page->mapping) {
- unlock_page(page);
- page_cache_release(page);
- goto find_page;
- }
- ret = -EIO;
- goto out;
- }
- } else
- SetPageUptodate(page);
- }
- }
-
- ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
- if (unlikely(ret)) {
- loff_t isize = i_size_read(mapping->host);
-
- if (ret != AOP_TRUNCATED_PAGE)
- unlock_page(page);
- page_cache_release(page);
- if (ret == AOP_TRUNCATED_PAGE)
- goto find_page;
-
- /*
- * prepare_write() may have instantiated a few blocks
- * outside i_size. Trim these off again.
- */
- if (sd->pos + this_len > isize)
- vmtruncate(mapping->host, isize);
-
- goto out_ret;
- }
+ ret = pagecache_write_begin(file, mapping, sd->pos, sd->len, 0, &page, &fsdata);
+ if (unlikely(ret))
+ goto out;

if (buf->page != page) {
/*
@@ -676,28 +601,13 @@ find_page:
char *dst = kmap_atomic(page, KM_USER1);

memcpy(dst + offset, src + buf->offset, this_len);
- flush_dcache_page(page);
kunmap_atomic(dst, KM_USER1);
buf->ops->unmap(pipe, buf, src);
}

- ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
- if (!ret) {
- /*
- * Return the number of bytes written and mark page as
- * accessed, we are now done!
- */
- ret = this_len;
- mark_page_accessed(page);
- balance_dirty_pages_ratelimited(mapping);
- } else if (ret == AOP_TRUNCATED_PAGE) {
- page_cache_release(page);
- goto find_page;
- }
+ ret = pagecache_write_end(file, mapping, sd->pos, sd->len, sd->len, page, fsdata);
+
out:
- page_cache_release(page);
- unlock_page(page);
-out_ret:
return ret;
}

Index: linux-2.6/Documentation/filesystems/Locking
===================================================================
--- linux-2.6.orig/Documentation/filesystems/Locking
+++ linux-2.6/Documentation/filesystems/Locking
@@ -176,15 +176,18 @@ 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
Index: linux-2.6/Documentation/filesystems/vfs.txt
===================================================================
--- linux-2.6.orig/Documentation/filesystems/vfs.txt
+++ linux-2.6/Documentation/filesystems/vfs.txt
@@ -534,6 +534,14 @@ 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, int intr,
+ 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);
+ int (*perform_write)(struct file *, struct address_space *,
+ struct iov_iter *, loff_t);
sector_t (*bmap)(struct address_space *, sector_t);
int (*invalidatepage) (struct page *, unsigned long);
int (*releasepage) (struct page *, int);
@@ -629,6 +637,36 @@ 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. Called
+ by the generic buffered write code to ask the filesystem to prepare
+ to write len bytes at the given offset in the file. intr is a boolean
+ that specifies whether or not the filesystem must be prepared to
+ handle a short write (ie. write_end called with less than len bytes
+ written).
+
+ The filesystem must return the locked pagecache page for the caller
+ to write into.
+
+ A void * may be returned in fsdata, which then gets passed into
+ write_end.
+
+ Returns < 0 on failure, in which case all cleanup must be done and
+ write_end not called. 0 on success, in which case write_end must
+ be 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 (they must be equal if
+ write_begin was called with intr == 0).
+
+ The filesystem must take care of unlocking the page and dropping its
+ refcount, and updating i_size.
+
+ Returns < 0 on failure, otherwise the number of bytes (<= 'copied')
+ that were able to be copied into the file.
+
+ perform_write:
+
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
-
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