[PATCH 02/17] vfs: Export __generic_file_aio_write() and add some comments

Jan Kara
2009-08-21T17:24:20Z

Rename __generic_file_aio_write_nolock() to __generic_file_aio_write(), add
comments to write helpers explaining how they should be used and export
__generic_file_aio_write() since it will be used by some filesystems.

CC: ocfs2-devel@oss.oracle.com
CC: Joel Becker <joel.becker@oracle.com>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
---
include/linux/fs.h | 2 +
mm/filemap.c | 57 +++++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 52 insertions(+), 7 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index cb365ad..1edd159 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2195,6 +2195,8 @@ extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
extern int file_read_actor(read_descriptor_t * desc, struct page *page, unsigned long offset, unsigned long size);
int generic_write_checks(struct file *file, loff_t *pos, size_t *count, int isblk);
extern ssize_t generic_file_aio_read(struct kiocb *, const struct iovec *, unsigned long, loff_t);
+extern ssize_t __generic_file_aio_write(struct kiocb *, const struct iovec *, unsigned long,
+ loff_t *);
extern ssize_t generic_file_aio_write(struct kiocb *, const struct iovec *, unsigned long, loff_t);
extern ssize_t generic_file_aio_write_nolock(struct kiocb *, const struct iovec *,
unsigned long, loff_t);
diff --git a/mm/filemap.c b/mm/filemap.c
index 65b2e50..554a396 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2368,9 +2368,27 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
}
EXPORT_SYMBOL(generic_file_buffered_write);

-static ssize_t
-__generic_file_aio_write_nolock(struct kiocb *iocb, const struct iovec *iov,
- unsigned long nr_segs, loff_t *ppos)
+/**
+ * __generic_file_aio_write - write data to a file
+ * @iocb: IO state structure (file, offset, etc.)
+ * @iov: vector with data to write
+ * @nr_segs: number of segments in the vector
+ * @ppos: position where to write
+ *
+ * This function does all the work needed for actually writing data to a
+ * file. It does all basic checks, removes SUID from the file, updates
+ * modification times and calls proper subroutines depending on whether we
+ * do direct IO or a standard buffered write.
+ *
+ * It expects i_mutex to be grabbed unless we work on a block device or similar
+ * object which does not need locking at all.
+ *
+ * This function does *not* take care of syncing data in case of O_SYNC write.
+ * A caller has to handle it. This is mainly due to the fact that we want to
+ * avoid syncing under i_mutex.
+ */
+ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
+ unsigned long nr_segs, loff_t *ppos)
{
struct file *file = iocb->ki_filp;
struct address_space * mapping = file->f_mapping;
@@ -2467,7 +2485,23 @@ out:
current->backing_dev_info = NULL;
return written ? written : err;
}
+EXPORT_SYMBOL(__generic_file_aio_write);
+

+/**
+ * generic_file_aio_write_nolock - write data, usually to a device
+ * @iocb: IO state structure
+ * @iov: vector with data to write
+ * @nr_segs: number of segments in the vector
+ * @pos: position in file where to write
+ *
+ * This is a wrapper around __generic_file_aio_write() which takes care of
+ * syncing the file in case of O_SYNC file. It does not take i_mutex for the
+ * write itself but may do so during syncing. It is meant for users like block
+ * devices which do not need i_mutex during write. If your filesystem needs to
+ * do a write but already holds i_mutex, use __generic_file_aio_write()
+ * directly and then sync the file like generic_file_aio_write().
+ */
ssize_t generic_file_aio_write_nolock(struct kiocb *iocb,
const struct iovec *iov, unsigned long nr_segs, loff_t pos)
{
@@ -2478,8 +2512,7 @@ ssize_t generic_file_aio_write_nolock(struct kiocb *iocb,

BUG_ON(iocb->ki_pos != pos);

- ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
- &iocb->ki_pos);
+ ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);

if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
ssize_t err;
@@ -2492,6 +2525,17 @@ ssize_t generic_file_aio_write_nolock(struct kiocb *iocb,
}
EXPORT_SYMBOL(generic_file_aio_write_nolock);

+/**
+ * generic_file_aio_write - write data to a file
+ * @iocb: IO state structure
+ * @iov: vector with data to write
+ * @nr_segs: number of segments in the vector
+ * @pos: position in file where to write
+ *
+ * This is a wrapper around __generic_file_aio_write() to be used by most
+ * filesystems. It takes care of syncing the file in case of O_SYNC file
+ * and acquires i_mutex as needed.
+ */
ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
unsigned long nr_segs, loff_t pos)
{
@@ -2503,8 +2547,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
BUG_ON(iocb->ki_pos != pos);

mutex_lock(&inode->i_mutex);
- ret = __generic_file_aio_write_nolock(iocb, iov, nr_segs,
- &iocb->ki_pos);
+ ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
mutex_unlock(&inode->i_mutex);

if (ret > 0 && ((file->f_flags & O_SYNC) || IS_SYNC(inode))) {
--
1.6.0.2