iov_iter_truncate()

Now It Can Be Done(tm) - we don't need to do iov_shorten() in
generic_file_direct_write() anymore, now that all ->direct_IO()
instances are converted to proper iov_iter methods and honour
iter->count and iter->iov_offset properly.

Get rid of count/ocount arguments of generic_file_direct_write(),
while we are at it.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/btrfs/file.c

@@ -1659,8 +1659,7 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
 
 static ssize_t __btrfs_direct_write(struct kiocb *iocb,
 				    struct iov_iter *from,
-				    loff_t pos,
-				    size_t count, size_t ocount)
+				    loff_t pos)
 {
 	struct file *file = iocb->ki_filp;
 	ssize_t written;
@@ -1668,9 +1667,9 @@ static ssize_t __btrfs_direct_write(struct kiocb *iocb,
 	loff_t endbyte;
 	int err;
 
-	written = generic_file_direct_write(iocb, from, pos, count, ocount);
+	written = generic_file_direct_write(iocb, from, pos);
 
-	if (written < 0 || written == count)
+	if (written < 0 || !iov_iter_count(from))
 		return written;
 
 	pos += written;
@@ -1720,13 +1719,14 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	u64 end_pos;
 	ssize_t num_written = 0;
 	ssize_t err = 0;
-	size_t count, ocount;
+	size_t count;
 	bool sync = (file->f_flags & O_DSYNC) || IS_SYNC(file->f_mapping->host);
 	struct iov_iter i;
 
 	mutex_lock(&inode->i_mutex);
 
-	count = ocount = iov_length(iov, nr_segs);
+	count = iov_length(iov, nr_segs);
+	iov_iter_init(&i, WRITE, iov, nr_segs, count);
 
 	current->backing_dev_info = inode->i_mapping->backing_dev_info;
 	err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
@@ -1740,7 +1740,7 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 		goto out;
 	}
 
-	iov_iter_init(&i, WRITE, iov, nr_segs, count);
+	iov_iter_truncate(&i, count);
 
 	err = file_remove_suid(file);
 	if (err) {
@@ -1783,8 +1783,7 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 		atomic_inc(&BTRFS_I(inode)->sync_writers);
 
 	if (unlikely(file->f_flags & O_DIRECT)) {
-		num_written = __btrfs_direct_write(iocb, &i,
-						   pos, count, ocount);
+		num_written = __btrfs_direct_write(iocb, &i, pos);
 	} else {
 		num_written = __btrfs_buffered_write(file, &i, pos);
 		if (num_written > 0)

fs/fuse/file.c

@@ -1188,8 +1188,7 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 {
 	struct file *file = iocb->ki_filp;
 	struct address_space *mapping = file->f_mapping;
-	size_t count = 0;
-	size_t ocount = 0;
+	size_t count;
 	ssize_t written = 0;
 	ssize_t written_buffered = 0;
 	struct inode *inode = mapping->host;
@@ -1208,7 +1207,8 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 
 	WARN_ON(iocb->ki_pos != pos);
 
-	count = ocount = iov_length(iov, nr_segs);
+	count = iov_length(iov, nr_segs);
+	iov_iter_init(&i, WRITE, iov, nr_segs, count);
 	mutex_lock(&inode->i_mutex);
 
 	/* We can write back this queue in page reclaim */
@@ -1217,11 +1217,11 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
 	if (err)
 		goto out;
-	iov_iter_init(&i, WRITE, iov, nr_segs, count);
 
 	if (count == 0)
 		goto out;
 
+	iov_iter_truncate(&i, count);
 	err = file_remove_suid(file);
 	if (err)
 		goto out;
@@ -1231,8 +1231,8 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 		goto out;
 
 	if (file->f_flags & O_DIRECT) {
-		written = generic_file_direct_write(iocb, &i, pos, count, ocount);
-		if (written < 0 || written == count)
+		written = generic_file_direct_write(iocb, &i, pos);
+		if (written < 0 || !iov_iter_count(&i))
 			goto out;
 
 		pos += written;
@@ -1469,8 +1469,7 @@ static ssize_t __fuse_direct_write(struct fuse_io_priv *io,
 
 	res = generic_write_checks(file, ppos, &count, 0);
 	if (!res) {
-		if (iter->count > count)
-			iter->count = count;
+		iov_iter_truncate(iter, count);
 		res = fuse_direct_io(io, iter, ppos, FUSE_DIO_WRITE);
 	}
 
@@ -2896,8 +2895,7 @@ fuse_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
 		if (offset >= i_size)
 			return 0;
 		count = min_t(loff_t, count, fuse_round_up(i_size - offset));
-		if (iter->count > count)
-			iter->count = count;
+		iov_iter_truncate(iter, count);
 	}
 
 	io = kmalloc(sizeof(struct fuse_io_priv), GFP_KERNEL);

fs/ocfs2/file.c

@@ -2241,7 +2241,6 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 	int ret, direct_io, appending, rw_level, have_alloc_sem  = 0;
 	int can_do_direct, has_refcount = 0;
 	ssize_t written = 0;
-	size_t ocount;		/* original count */
 	size_t count;		/* after file limit checks */
 	loff_t old_size, *ppos = &iocb->ki_pos;
 	u32 old_clusters;
@@ -2253,6 +2252,9 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 	int unaligned_dio = 0;
 	struct iov_iter from;
 
+	count = iov_length(iov, nr_segs);
+	iov_iter_init(&from, WRITE, iov, nr_segs, count);
+
 	trace_ocfs2_file_aio_write(inode, file, file->f_path.dentry,
 		(unsigned long long)OCFS2_I(inode)->ip_blkno,
 		file->f_path.dentry->d_name.len,
@@ -2355,16 +2357,14 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 	/* communicate with ocfs2_dio_end_io */
 	ocfs2_iocb_set_rw_locked(iocb, rw_level);
 
-	count = ocount = iov_length(iov, nr_segs);
 	ret = generic_write_checks(file, ppos, &count,
 				   S_ISBLK(inode->i_mode));
 	if (ret)
 		goto out_dio;
 
-	iov_iter_init(&from, WRITE, iov, nr_segs, count);
+	iov_iter_truncate(&from, count);
 	if (direct_io) {
-		written = generic_file_direct_write(iocb, &from, *ppos,
-						    count, ocount);
+		written = generic_file_direct_write(iocb, &from, *ppos);
 		if (written < 0) {
 			ret = written;
 			goto out_dio;

fs/xfs/xfs_file.c

@@ -626,7 +626,7 @@ xfs_file_dio_aio_write(
 	const struct iovec	*iovp,
 	unsigned long		nr_segs,
 	loff_t			pos,
-	size_t			ocount)
+	size_t			count)
 {
 	struct file		*file = iocb->ki_filp;
 	struct address_space	*mapping = file->f_mapping;
@@ -634,7 +634,6 @@ xfs_file_dio_aio_write(
 	struct xfs_inode	*ip = XFS_I(inode);
 	struct xfs_mount	*mp = ip->i_mount;
 	ssize_t			ret = 0;
-	size_t			count = ocount;
 	int			unaligned_io = 0;
 	int			iolock;
 	struct xfs_buftarg	*target = XFS_IS_REALTIME_INODE(ip) ?
@@ -645,6 +644,8 @@ xfs_file_dio_aio_write(
 	if ((pos | count) & target->bt_logical_sectormask)
 		return -XFS_ERROR(EINVAL);
 
+	iov_iter_init(&from, WRITE, iovp, nr_segs, count);
+
 	/* "unaligned" here means not aligned to a filesystem block */
 	if ((pos & mp->m_blockmask) || ((pos + count) & mp->m_blockmask))
 		unaligned_io = 1;
@@ -676,6 +677,7 @@ xfs_file_dio_aio_write(
 	ret = xfs_file_aio_write_checks(file, &pos, &count, &iolock);
 	if (ret)
 		goto out;
+	iov_iter_truncate(&from, count);
 
 	if (mapping->nrpages) {
 		ret = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
@@ -697,8 +699,7 @@ xfs_file_dio_aio_write(
 	}
 
 	trace_xfs_file_direct_write(ip, count, iocb->ki_pos, 0);
-	iov_iter_init(&from, WRITE, iovp, nr_segs, count);
-	ret = generic_file_direct_write(iocb, &from, pos, count, ocount);
+	ret = generic_file_direct_write(iocb, &from, pos);
 
 out:
 	xfs_rw_iunlock(ip, iolock);

include/linux/fs.h

@@ -2407,8 +2407,7 @@ extern ssize_t generic_file_aio_read(struct kiocb *, const struct iovec *, unsig
 extern ssize_t generic_file_read_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t __generic_file_aio_write(struct kiocb *, const struct iovec *, unsigned long);
 extern ssize_t generic_file_aio_write(struct kiocb *, const struct iovec *, unsigned long, loff_t);
-extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *,
-		loff_t, size_t, size_t);
+extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *, loff_t);
 extern ssize_t generic_perform_write(struct file *, struct iov_iter *, loff_t);
 extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);
 extern ssize_t do_sync_write(struct file *filp, const char __user *buf, size_t len, loff_t *ppos);

include/linux/uio.h

@@ -82,6 +82,12 @@ static inline size_t iov_iter_count(struct iov_iter *i)
 	return i->count;
 }
 
+static inline void iov_iter_truncate(struct iov_iter *i, size_t count)
+{
+	if (i->count > count)
+		i->count = count;
+}
+
 int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
 int memcpy_toiovec(struct iovec *iov, unsigned char *kdata, int len);
 

mm/filemap.c

@@ -2345,8 +2345,7 @@ int pagecache_write_end(struct file *file, struct address_space *mapping,
 EXPORT_SYMBOL(pagecache_write_end);
 
 ssize_t
-generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
-		loff_t pos, size_t count, size_t ocount)
+generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos)
 {
 	struct file	*file = iocb->ki_filp;
 	struct address_space *mapping = file->f_mapping;
@@ -2356,10 +2355,7 @@ generic_file_direct_write(struct kiocb *iocb, struct iov_iter *from,
 	pgoff_t		end;
 	struct iov_iter data;
 
-	if (count != ocount)
-		from->nr_segs = iov_shorten((struct iovec *)from->iov, from->nr_segs, count);
-
-	write_len = iov_length(from->iov, from->nr_segs);
+	write_len = iov_iter_count(from);
 	end = (pos + write_len - 1) >> PAGE_CACHE_SHIFT;
 
 	written = filemap_write_and_wait_range(mapping, pos, pos + write_len - 1);
@@ -2568,7 +2564,6 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 {
 	struct file *file = iocb->ki_filp;
 	struct address_space * mapping = file->f_mapping;
-	size_t ocount;		/* original count */
 	size_t count;		/* after file limit checks */
 	struct inode 	*inode = mapping->host;
 	loff_t		pos = iocb->ki_pos;
@@ -2577,7 +2572,8 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	ssize_t		status;
 	struct iov_iter from;
 
-	count = ocount = iov_length(iov, nr_segs);
+	count = iov_length(iov, nr_segs);
+	iov_iter_init(&from, WRITE, iov, nr_segs, count);
 
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
@@ -2588,6 +2584,8 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	if (count == 0)
 		goto out;
 
+	iov_iter_truncate(&from, count);
+
 	err = file_remove_suid(file);
 	if (err)
 		goto out;
@@ -2596,14 +2594,11 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	if (err)
 		goto out;
 
-	iov_iter_init(&from, WRITE, iov, nr_segs, count);
-
 	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
 	if (unlikely(file->f_flags & O_DIRECT)) {
 		loff_t endbyte;
 
-		written = generic_file_direct_write(iocb, &from, pos,
-							count, ocount);
+		written = generic_file_direct_write(iocb, &from, pos);
 		if (written < 0 || written == count)
 			goto out;