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SubjectRe: [patch 2/5] fs: introduce new aops and infrastructure
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Date
Nick Piggin <npiggin@suse.de> writes:

> 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;
If prepare_write succeed we return with locked and getted page, let's remember it as [1]
> + }
> +}
> +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;
What about AOP_TRUNCATED_PAGE? Off corse we can't just "goto retry" here :) ,
but we may return it to caller and let's caller handle it.
> + }
> +
> + return copied;
if ->commit_write return non negative value we return with sill locked page look above at [1]
may be it will be unlocked by caller? I guess no it was just forgoten.
> +}
> +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;
WOW caller forgot unlock page too see above at [1].
> +
> + 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;__block_prepare_write
> +
> + 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);
<<<<OOPS why you new block wasn't fully zeroed? as it was done before.
At least this result in information leak in case of (stat == from)
just imagine fs with blocksize == 1k conains file with i_size == 4096 and
fist two blocks not mapped (hole), now invoke write op from 1023 to 2048.
For example we succeed in allocating first block, but faile while allocating second
, then we call page_zero_new_buffers(...from == 1023, to == 2048)
and then zerro only one last byte for first block, and set is uptodate
After this we just do read( from == 0, to == 1023) and steal old block content.

> + 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;
<<<<<< BTW: do_lo_send_aops() code itself is realy ugly, for example patrial
write not supported.
> - }
> 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
Ohhh and now i'm totaly shure what you just forgot unlocking stuff
in pagecache_write_end()
> +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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