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fs: introduce write_begin, write_end, and perform_write aops

Browse source 
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>
This commit is contained in:
Nick Piggin 2007-10-16 01:25:01 -07:00 • committed by Linus Torvalds
parent 637aff46f9
commit afddba49d1
11 changed files with 575 additions and 206 deletions
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250
mm/filemap.c
View file

@ -1742,11 +1742,20 @@ void iov_iter_advance(struct iov_iter *i, size_t bytes)
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 @@ inline int generic_write_checks(struct file *file, loff_t *pos, size_t *count, i
}
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 @@ 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;
@ -1908,20 +2005,16 @@ repeat:
}
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 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
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 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
* 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 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
* 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 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
page_cache_release(src_page);
continue;
}
}
status = a_ops->prepare_write(file, page, offset, offset+bytes);
@ -2030,7 +2122,7 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
* 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 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
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 @@ 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, 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);
/*
* 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,