fs: 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).
[mark.fasheh@oracle.com: API design contributions, code review and fixes]
[akpm@linux-foundation.org: various fixes]
[dmonakhov@sw.ru: new aop block_write_begin fix]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Dmitriy Monakhov <dmonakhov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap.c b/mm/filemap.c
index 67a03a0..ec25ba1 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1742,11 +1742,20 @@
i->count -= bytes;
}
-int iov_iter_fault_in_readable(struct iov_iter *i)
+/*
+ * Fault in the first iovec of the given iov_iter, to a maximum length
+ * of bytes. Returns 0 on success, or non-zero if the memory could not be
+ * accessed (ie. because it is an invalid address).
+ *
+ * writev-intensive code may want this to prefault several iovecs -- that
+ * would be possible (callers must not rely on the fact that _only_ the
+ * first iovec will be faulted with the current implementation).
+ */
+int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
{
- size_t seglen = min(i->iov->iov_len - i->iov_offset, i->count);
char __user *buf = i->iov->iov_base + i->iov_offset;
- return fault_in_pages_readable(buf, seglen);
+ bytes = min(bytes, i->iov->iov_len - i->iov_offset);
+ return fault_in_pages_readable(buf, bytes);
}
/*
@@ -1843,6 +1852,95 @@
}
EXPORT_SYMBOL(generic_write_checks);
+int pagecache_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned flags,
+ 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, flags,
+ 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 (flags & AOP_FLAG_UNINTERRUPTIBLE && !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_end) {
+ mark_page_accessed(page);
+ ret = aops->write_end(file, mapping, pos, len, copied,
+ page, fsdata);
+ } else {
+ 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);
+ unlock_page(page);
+ mark_page_accessed(page);
+ page_cache_release(page);
+ BUG_ON(ret == AOP_TRUNCATED_PAGE); /* can't deal with */
+
+ if (ret < 0) {
+ if (pos + len > inode->i_size)
+ vmtruncate(inode, inode->i_size);
+ } else if (ret > 0)
+ ret = min_t(size_t, copied, ret);
+ else
+ ret = copied;
+ }
+
+ return ret;
+}
+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,
@@ -1886,8 +1984,7 @@
* 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;
@@ -1908,20 +2005,16 @@
}
return page;
}
+EXPORT_SYMBOL(__grab_cache_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;
@@ -1934,7 +2027,7 @@
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
@@ -1952,7 +2045,7 @@
* 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, bytes))) {
status = -EFAULT;
break;
}
@@ -1983,7 +2076,7 @@
* 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;
@@ -2008,7 +2101,6 @@
page_cache_release(src_page);
continue;
}
-
}
status = a_ops->prepare_write(file, page, offset, offset+bytes);
@@ -2030,7 +2122,7 @@
* 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 {
@@ -2056,9 +2148,9 @@
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();
@@ -2082,13 +2174,117 @@
continue;
else
break;
- } while (iov_iter_count(&i));
- *ppos = pos;
+ } while (iov_iter_count(i));
- /*
- * For now, when the user asks for O_SYNC, we'll actually give O_DSYNC
- */
+ 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, bytes))) {
+ status = -EFAULT;
+ break;
+ }
+
+ status = a_ops->write_begin(file, mapping, pos, bytes, 0,
+ &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;
+ ssize_t status;
+ struct iov_iter i;
+
+ iov_iter_init(&i, iov, nr_segs, count, written);
+ if (a_ops->write_begin)
+ status = generic_perform_write(file, &i, pos);
+ else
+ status = generic_perform_write_2copy(file, &i, pos);
+
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,