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Date: Mon, 3 Dec 2012 11:36:36 +0100 (CET)
From: Lukáš Czerner <lczerner@...hat.com>
To: "Theodore Ts'o" <tytso@....edu>
cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: restructure ext4_ext_direct_IO()
On Thu, 29 Nov 2012, Theodore Ts'o wrote:
> Date: Thu, 29 Nov 2012 21:17:06 -0500
> From: Theodore Ts'o <tytso@....edu>
> To: Ext4 Developers List <linux-ext4@...r.kernel.org>
> Cc: Theodore Ts'o <tytso@....edu>
> Subject: [PATCH] ext4: restructure ext4_ext_direct_IO()
>
> Remove a level of indentation by moving the DIO read and extending
> write case to the beginning of the file. This results in no actual
> programmatic changes to the file, but makes it easier to
> read/understand.
>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
Looks good.
Reviewed-by: Lukas Czerner <lczerner@...hat.com>
Thanks!
-Lukas
> ---
> fs/ext4/inode.c | 211 +++++++++++++++++++++++++++-----------------------------
> 1 file changed, 103 insertions(+), 108 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index cf5d30a..91a2496 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2927,10 +2927,10 @@ retry:
> * fall back to buffered IO.
> *
> * For holes, we fallocate those blocks, mark them as uninitialized
> - * If those blocks were preallocated, we mark sure they are splited, but
> + * If those blocks were preallocated, we mark sure they are split, but
> * still keep the range to write as uninitialized.
> *
> - * The unwrritten extents will be converted to written when DIO is completed.
> + * The unwritten extents will be converted to written when DIO is completed.
> * For async direct IO, since the IO may still pending when return, we
> * set up an end_io call back function, which will do the conversion
> * when async direct IO completed.
> @@ -2948,125 +2948,120 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb,
> struct inode *inode = file->f_mapping->host;
> ssize_t ret;
> size_t count = iov_length(iov, nr_segs);
> -
> + int overwrite = 0;
> + get_block_t *get_block_func = NULL;
> + int dio_flags = 0;
> loff_t final_size = offset + count;
> - if (rw == WRITE && final_size <= inode->i_size) {
> - int overwrite = 0;
> - get_block_t *get_block_func = NULL;
> - int dio_flags = 0;
>
> - BUG_ON(iocb->private == NULL);
> + /* Use the old path for reads and writes beyond i_size. */
> + if (rw != WRITE || final_size > inode->i_size)
> + return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
>
> - /* If we do a overwrite dio, i_mutex locking can be released */
> - overwrite = *((int *)iocb->private);
> + BUG_ON(iocb->private == NULL);
>
> - if (overwrite) {
> - atomic_inc(&inode->i_dio_count);
> - down_read(&EXT4_I(inode)->i_data_sem);
> - mutex_unlock(&inode->i_mutex);
> - }
> + /* If we do a overwrite dio, i_mutex locking can be released */
> + overwrite = *((int *)iocb->private);
>
> - /*
> - * We could direct write to holes and fallocate.
> - *
> - * Allocated blocks to fill the hole are marked as uninitialized
> - * to prevent parallel buffered read to expose the stale data
> - * before DIO complete the data IO.
> - *
> - * As to previously fallocated extents, ext4 get_block
> - * will just simply mark the buffer mapped but still
> - * keep the extents uninitialized.
> - *
> - * for non AIO case, we will convert those unwritten extents
> - * to written after return back from blockdev_direct_IO.
> - *
> - * for async DIO, the conversion needs to be defered when
> - * the IO is completed. The ext4 end_io callback function
> - * will be called to take care of the conversion work.
> - * Here for async case, we allocate an io_end structure to
> - * hook to the iocb.
> - */
> - iocb->private = NULL;
> - ext4_inode_aio_set(inode, NULL);
> - if (!is_sync_kiocb(iocb)) {
> - ext4_io_end_t *io_end =
> - ext4_init_io_end(inode, GFP_NOFS);
> - if (!io_end) {
> - ret = -ENOMEM;
> - goto retake_lock;
> - }
> - io_end->flag |= EXT4_IO_END_DIRECT;
> - iocb->private = io_end;
> - /*
> - * we save the io structure for current async
> - * direct IO, so that later ext4_map_blocks()
> - * could flag the io structure whether there
> - * is a unwritten extents needs to be converted
> - * when IO is completed.
> - */
> - ext4_inode_aio_set(inode, io_end);
> - }
> + if (overwrite) {
> + atomic_inc(&inode->i_dio_count);
> + down_read(&EXT4_I(inode)->i_data_sem);
> + mutex_unlock(&inode->i_mutex);
> + }
>
> - if (overwrite) {
> - get_block_func = ext4_get_block_write_nolock;
> - } else {
> - get_block_func = ext4_get_block_write;
> - dio_flags = DIO_LOCKING;
> + /*
> + * We could direct write to holes and fallocate.
> + *
> + * Allocated blocks to fill the hole are marked as
> + * uninitialized to prevent parallel buffered read to expose
> + * the stale data before DIO complete the data IO.
> + *
> + * As to previously fallocated extents, ext4 get_block will
> + * just simply mark the buffer mapped but still keep the
> + * extents uninitialized.
> + *
> + * For non AIO case, we will convert those unwritten extents
> + * to written after return back from blockdev_direct_IO.
> + *
> + * For async DIO, the conversion needs to be deferred when the
> + * IO is completed. The ext4 end_io callback function will be
> + * called to take care of the conversion work. Here for async
> + * case, we allocate an io_end structure to hook to the iocb.
> + */
> + iocb->private = NULL;
> + ext4_inode_aio_set(inode, NULL);
> + if (!is_sync_kiocb(iocb)) {
> + ext4_io_end_t *io_end = ext4_init_io_end(inode, GFP_NOFS);
> + if (!io_end) {
> + ret = -ENOMEM;
> + goto retake_lock;
> }
> - ret = __blockdev_direct_IO(rw, iocb, inode,
> - inode->i_sb->s_bdev, iov,
> - offset, nr_segs,
> - get_block_func,
> - ext4_end_io_dio,
> - NULL,
> - dio_flags);
> -
> - if (iocb->private)
> - ext4_inode_aio_set(inode, NULL);
> + io_end->flag |= EXT4_IO_END_DIRECT;
> + iocb->private = io_end;
> /*
> - * The io_end structure takes a reference to the inode,
> - * that structure needs to be destroyed and the
> - * reference to the inode need to be dropped, when IO is
> - * complete, even with 0 byte write, or failed.
> - *
> - * In the successful AIO DIO case, the io_end structure will be
> - * desctroyed and the reference to the inode will be dropped
> - * after the end_io call back function is called.
> - *
> - * In the case there is 0 byte write, or error case, since
> - * VFS direct IO won't invoke the end_io call back function,
> - * we need to free the end_io structure here.
> + * we save the io structure for current async direct
> + * IO, so that later ext4_map_blocks() could flag the
> + * io structure whether there is a unwritten extents
> + * needs to be converted when IO is completed.
> */
> - if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
> - ext4_free_io_end(iocb->private);
> - iocb->private = NULL;
> - } else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
> - EXT4_STATE_DIO_UNWRITTEN)) {
> - int err;
> - /*
> - * for non AIO case, since the IO is already
> - * completed, we could do the conversion right here
> - */
> - err = ext4_convert_unwritten_extents(inode,
> - offset, ret);
> - if (err < 0)
> - ret = err;
> - ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
> - }
> + ext4_inode_aio_set(inode, io_end);
> + }
>
> - retake_lock:
> - /* take i_mutex locking again if we do a ovewrite dio */
> - if (overwrite) {
> - inode_dio_done(inode);
> - up_read(&EXT4_I(inode)->i_data_sem);
> - mutex_lock(&inode->i_mutex);
> - }
> + if (overwrite) {
> + get_block_func = ext4_get_block_write_nolock;
> + } else {
> + get_block_func = ext4_get_block_write;
> + dio_flags = DIO_LOCKING;
> + }
> + ret = __blockdev_direct_IO(rw, iocb, inode,
> + inode->i_sb->s_bdev, iov,
> + offset, nr_segs,
> + get_block_func,
> + ext4_end_io_dio,
> + NULL,
> + dio_flags);
> +
> + if (iocb->private)
> + ext4_inode_aio_set(inode, NULL);
> + /*
> + * The io_end structure takes a reference to the inode, that
> + * structure needs to be destroyed and the reference to the
> + * inode need to be dropped, when IO is complete, even with 0
> + * byte write, or failed.
> + *
> + * In the successful AIO DIO case, the io_end structure will
> + * be destroyed and the reference to the inode will be dropped
> + * after the end_io call back function is called.
> + *
> + * In the case there is 0 byte write, or error case, since VFS
> + * direct IO won't invoke the end_io call back function, we
> + * need to free the end_io structure here.
> + */
> + if (ret != -EIOCBQUEUED && ret <= 0 && iocb->private) {
> + ext4_free_io_end(iocb->private);
> + iocb->private = NULL;
> + } else if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
> + EXT4_STATE_DIO_UNWRITTEN)) {
> + int err;
> + /*
> + * for non AIO case, since the IO is already
> + * completed, we could do the conversion right here
> + */
> + err = ext4_convert_unwritten_extents(inode,
> + offset, ret);
> + if (err < 0)
> + ret = err;
> + ext4_clear_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
> + }
>
> - return ret;
> +retake_lock:
> + /* take i_mutex locking again if we do a ovewrite dio */
> + if (overwrite) {
> + inode_dio_done(inode);
> + up_read(&EXT4_I(inode)->i_data_sem);
> + mutex_lock(&inode->i_mutex);
> }
>
> - /* for write the the end of file case, we fall back to old way */
> - return ext4_ind_direct_IO(rw, iocb, iov, offset, nr_segs);
> + return ret;
> }
>
> static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
>
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