ext4: introduce direct I/O write using iomap infrastructure
This patch introduces a new direct I/O write path which makes use of
the iomap infrastructure.
All direct I/O writes are now passed from the ->write_iter() callback
through to the new direct I/O handler ext4_dio_write_iter(). This
function is responsible for calling into the iomap infrastructure via
iomap_dio_rw().
Code snippets from the existing direct I/O write code within
ext4_file_write_iter() such as, checking whether the I/O request is
unaligned asynchronous I/O, or whether the write will result in an
overwrite have effectively been moved out and into the new direct I/O
->write_iter() handler.
The block mapping flags that are eventually passed down to
ext4_map_blocks() from the *_get_block_*() suite of routines have been
taken out and introduced within ext4_iomap_alloc().
For inode extension cases, ext4_handle_inode_extension() is
effectively the function responsible for performing such metadata
updates. This is called after iomap_dio_rw() has returned so that we
can safely determine whether we need to potentially truncate any
allocated blocks that may have been prepared for this direct I/O
write. We don't perform the inode extension, or truncate operations
from the ->end_io() handler as we don't have the original I/O 'length'
available there. The ->end_io() however is responsible fo converting
allocated unwritten extents to written extents.
In the instance of a short write, we fallback and complete the
remainder of the I/O using buffered I/O via
ext4_buffered_write_iter().
The existing buffer_head direct I/O implementation has been removed as
it's now redundant.
[ Fix up ext4_dio_write_iter() per Jan's comments at
https://lore.kernel.org/r/20191105135932.GN22379@quack2.suse.cz -- TYT ]
Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/e55db6f12ae6ff017f36774135e79f3e7b0333da.1572949325.git.mbobrowski@mbobrowski.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 83ef9c9..6a7293a 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -29,6 +29,7 @@
#include <linux/pagevec.h>
#include <linux/uio.h>
#include <linux/mman.h>
+#include <linux/backing-dev.h>
#include "ext4.h"
#include "ext4_jbd2.h"
#include "xattr.h"
@@ -155,13 +156,6 @@ static int ext4_release_file(struct inode *inode, struct file *filp)
return 0;
}
-static void ext4_unwritten_wait(struct inode *inode)
-{
- wait_queue_head_t *wq = ext4_ioend_wq(inode);
-
- wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_unwritten) == 0));
-}
-
/*
* This tests whether the IO in question is block-aligned or not.
* Ext4 utilizes unwritten extents when hole-filling during direct IO, and they
@@ -214,13 +208,13 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
struct inode *inode = file_inode(iocb->ki_filp);
ssize_t ret;
+ if (unlikely(IS_IMMUTABLE(inode)))
+ return -EPERM;
+
ret = generic_write_checks(iocb, from);
if (ret <= 0)
return ret;
- if (unlikely(IS_IMMUTABLE(inode)))
- return -EPERM;
-
/*
* If we have encountered a bitmap-format file, the size limit
* is smaller than s_maxbytes, which is for extent-mapped files.
@@ -232,9 +226,42 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from)
return -EFBIG;
iov_iter_truncate(from, sbi->s_bitmap_maxbytes - iocb->ki_pos);
}
+
+ ret = file_modified(iocb->ki_filp);
+ if (ret)
+ return ret;
+
return iov_iter_count(from);
}
+static ssize_t ext4_buffered_write_iter(struct kiocb *iocb,
+ struct iov_iter *from)
+{
+ ssize_t ret;
+ struct inode *inode = file_inode(iocb->ki_filp);
+
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ return -EOPNOTSUPP;
+
+ inode_lock(inode);
+ ret = ext4_write_checks(iocb, from);
+ if (ret <= 0)
+ goto out;
+
+ current->backing_dev_info = inode_to_bdi(inode);
+ ret = generic_perform_write(iocb->ki_filp, from, iocb->ki_pos);
+ current->backing_dev_info = NULL;
+
+out:
+ inode_unlock(inode);
+ if (likely(ret > 0)) {
+ iocb->ki_pos += ret;
+ ret = generic_write_sync(iocb, ret);
+ }
+
+ return ret;
+}
+
static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset,
ssize_t written, size_t count)
{
@@ -316,6 +343,139 @@ static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset,
return written;
}
+static int ext4_dio_write_end_io(struct kiocb *iocb, ssize_t size,
+ int error, unsigned int flags)
+{
+ loff_t offset = iocb->ki_pos;
+ struct inode *inode = file_inode(iocb->ki_filp);
+
+ if (error)
+ return error;
+
+ if (size && flags & IOMAP_DIO_UNWRITTEN)
+ return ext4_convert_unwritten_extents(NULL, inode,
+ offset, size);
+
+ return 0;
+}
+
+static const struct iomap_dio_ops ext4_dio_write_ops = {
+ .end_io = ext4_dio_write_end_io,
+};
+
+static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
+{
+ ssize_t ret;
+ size_t count;
+ loff_t offset;
+ handle_t *handle;
+ struct inode *inode = file_inode(iocb->ki_filp);
+ bool extend = false, overwrite = false, unaligned_aio = false;
+
+ if (iocb->ki_flags & IOCB_NOWAIT) {
+ if (!inode_trylock(inode))
+ return -EAGAIN;
+ } else {
+ inode_lock(inode);
+ }
+
+ if (!ext4_dio_supported(inode)) {
+ inode_unlock(inode);
+ /*
+ * Fallback to buffered I/O if the inode does not support
+ * direct I/O.
+ */
+ return ext4_buffered_write_iter(iocb, from);
+ }
+
+ ret = ext4_write_checks(iocb, from);
+ if (ret <= 0) {
+ inode_unlock(inode);
+ return ret;
+ }
+
+ /*
+ * Unaligned asynchronous direct I/O must be serialized among each
+ * other as the zeroing of partial blocks of two competing unaligned
+ * asynchronous direct I/O writes can result in data corruption.
+ */
+ offset = iocb->ki_pos;
+ count = iov_iter_count(from);
+ if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
+ !is_sync_kiocb(iocb) && ext4_unaligned_aio(inode, from, offset)) {
+ unaligned_aio = true;
+ inode_dio_wait(inode);
+ }
+
+ /*
+ * Determine whether the I/O will overwrite allocated and initialized
+ * blocks. If so, check to see whether it is possible to take the
+ * dioread_nolock path.
+ */
+ if (!unaligned_aio && ext4_overwrite_io(inode, offset, count) &&
+ ext4_should_dioread_nolock(inode)) {
+ overwrite = true;
+ downgrade_write(&inode->i_rwsem);
+ }
+
+ if (offset + count > EXT4_I(inode)->i_disksize) {
+ handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
+ if (IS_ERR(handle)) {
+ ret = PTR_ERR(handle);
+ goto out;
+ }
+
+ ret = ext4_orphan_add(handle, inode);
+ if (ret) {
+ ext4_journal_stop(handle);
+ goto out;
+ }
+
+ extend = true;
+ ext4_journal_stop(handle);
+ }
+
+ ret = iomap_dio_rw(iocb, from, &ext4_iomap_ops, &ext4_dio_write_ops,
+ is_sync_kiocb(iocb) || unaligned_aio || extend);
+
+ if (extend)
+ ret = ext4_handle_inode_extension(inode, offset, ret, count);
+
+out:
+ if (overwrite)
+ inode_unlock_shared(inode);
+ else
+ inode_unlock(inode);
+
+ if (ret >= 0 && iov_iter_count(from)) {
+ ssize_t err;
+ loff_t endbyte;
+
+ offset = iocb->ki_pos;
+ err = ext4_buffered_write_iter(iocb, from);
+ if (err < 0)
+ return err;
+
+ /*
+ * We need to ensure that the pages within the page cache for
+ * the range covered by this I/O are written to disk and
+ * invalidated. This is in attempt to preserve the expected
+ * direct I/O semantics in the case we fallback to buffered I/O
+ * to complete off the I/O request.
+ */
+ ret += err;
+ endbyte = offset + err - 1;
+ err = filemap_write_and_wait_range(iocb->ki_filp->f_mapping,
+ offset, endbyte);
+ if (!err)
+ invalidate_mapping_pages(iocb->ki_filp->f_mapping,
+ offset >> PAGE_SHIFT,
+ endbyte >> PAGE_SHIFT);
+ }
+
+ return ret;
+}
+
#ifdef CONFIG_FS_DAX
static ssize_t
ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
@@ -332,15 +492,10 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
return -EAGAIN;
inode_lock(inode);
}
+
ret = ext4_write_checks(iocb, from);
if (ret <= 0)
goto out;
- ret = file_remove_privs(iocb->ki_filp);
- if (ret)
- goto out;
- ret = file_update_time(iocb->ki_filp);
- if (ret)
- goto out;
offset = iocb->ki_pos;
count = iov_iter_count(from);
@@ -378,10 +533,6 @@ static ssize_t
ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
struct inode *inode = file_inode(iocb->ki_filp);
- int o_direct = iocb->ki_flags & IOCB_DIRECT;
- int unaligned_aio = 0;
- int overwrite = 0;
- ssize_t ret;
if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
return -EIO;
@@ -390,59 +541,10 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
if (IS_DAX(inode))
return ext4_dax_write_iter(iocb, from);
#endif
+ if (iocb->ki_flags & IOCB_DIRECT)
+ return ext4_dio_write_iter(iocb, from);
- if (!inode_trylock(inode)) {
- if (iocb->ki_flags & IOCB_NOWAIT)
- return -EAGAIN;
- inode_lock(inode);
- }
-
- ret = ext4_write_checks(iocb, from);
- if (ret <= 0)
- goto out;
-
- /*
- * Unaligned direct AIO must be serialized among each other as zeroing
- * of partial blocks of two competing unaligned AIOs can result in data
- * corruption.
- */
- if (o_direct && ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
- !is_sync_kiocb(iocb) &&
- ext4_unaligned_aio(inode, from, iocb->ki_pos)) {
- unaligned_aio = 1;
- ext4_unwritten_wait(inode);
- }
-
- iocb->private = &overwrite;
- /* Check whether we do a DIO overwrite or not */
- if (o_direct && !unaligned_aio) {
- if (ext4_overwrite_io(inode, iocb->ki_pos, iov_iter_count(from))) {
- if (ext4_should_dioread_nolock(inode))
- overwrite = 1;
- } else if (iocb->ki_flags & IOCB_NOWAIT) {
- ret = -EAGAIN;
- goto out;
- }
- }
-
- ret = __generic_file_write_iter(iocb, from);
- /*
- * Unaligned direct AIO must be the only IO in flight. Otherwise
- * overlapping aligned IO after unaligned might result in data
- * corruption.
- */
- if (ret == -EIOCBQUEUED && unaligned_aio)
- ext4_unwritten_wait(inode);
- inode_unlock(inode);
-
- if (ret > 0)
- ret = generic_write_sync(iocb, ret);
-
- return ret;
-
-out:
- inode_unlock(inode);
- return ret;
+ return ext4_buffered_write_iter(iocb, from);
}
#ifdef CONFIG_FS_DAX