Re: [PATCH 4/4] vfs: RWF_NONBLOCK flag for preadv2

From: Steve French
Date: Mon Oct 27 2014 - 15:15:40 EST

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In reply to: Christoph Hellwig: "Re: [PATCH 4/4] vfs: RWF_NONBLOCK flag for preadv2"
Next in thread: Milosz Tanski: "Re: [PATCH 4/4] vfs: RWF_NONBLOCK flag for preadv2"
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What would be required for a network file system to support the
RWF_NONBLOCK flag?

SMB3 operations are all async (on the wire) by default but they do
block on the network send and interim response.

On Tue, Oct 21, 2014 at 3:46 PM, Milosz Tanski <milosz@xxxxxxxxx> wrote:
> Filesystems that generic_file_read_iter will not be allowed to perform
> non-blocking reads. This only will read data if it's in the page cache and if
> there is no page error (causing a re-read).
>
> Christoph Hellwig wrote the filesystem specify code (cifs, ofs, shm, xfs).
>
> Signed-off-by: Milosz Tanski <milosz@xxxxxxxxx>
> ---
> fs/cifs/file.c | 6 ++++++
> fs/ocfs2/file.c | 6 ++++++
> fs/pipe.c | 3 ++-
> fs/read_write.c | 21 ++++++++++++++-------
> fs/xfs/xfs_file.c | 4 ++++
> include/linux/fs.h | 3 +++
> mm/filemap.c | 18 ++++++++++++++++++
> mm/shmem.c | 4 ++++
> 8 files changed, 57 insertions(+), 8 deletions(-)
>
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 3e4d00a..c485afa 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -3005,6 +3005,9 @@ ssize_t cifs_user_readv(struct kiocb *iocb, struct iov_iter *to)
> struct cifs_readdata *rdata, *tmp;
> struct list_head rdata_list;
>
> + if (iocb->ki_rwflags & RWF_NONBLOCK)
> + return -EAGAIN;
> +
> len = iov_iter_count(to);
> if (!len)
> return 0;
> @@ -3123,6 +3126,9 @@ cifs_strict_readv(struct kiocb *iocb, struct iov_iter *to)
> ((cifs_sb->mnt_cifs_flags & CIFS_MOUNT_NOPOSIXBRL) == 0))
> return generic_file_read_iter(iocb, to);
>
> + if (iocb->ki_rwflags & RWF_NONBLOCK)
> + return -EAGAIN;
> +
> /*
> * We need to hold the sem to be sure nobody modifies lock list
> * with a brlock that prevents reading.
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index 324dc93..bb66ca4 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2472,6 +2472,12 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
> filp->f_path.dentry->d_name.name,
> to->nr_segs); /* GRRRRR */
>
> + /*
> + * No non-blocking reads for ocfs2 for now. Might be doable with
> + * non-blocking cluster lock helpers.
> + */
> + if (iocb->ki_rwflags & RWF_NONBLOCK)
> + return -EAGAIN;
>
> if (!inode) {
> ret = -EINVAL;
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 21981e5..212bf68 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -302,7 +302,8 @@ pipe_read(struct kiocb *iocb, struct iov_iter *to)
> */
> if (ret)
> break;
> - if (filp->f_flags & O_NONBLOCK) {
> + if ((filp->f_flags & O_NONBLOCK) ||
> + (iocb->ki_rwflags & RWF_NONBLOCK)) {
> ret = -EAGAIN;
> break;
> }
> diff --git a/fs/read_write.c b/fs/read_write.c
> index e3d8451..955d829 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -835,14 +835,19 @@ static ssize_t do_readv_writev(int type, struct file *file,
> file_start_write(file);
> }
>
> - if (iter_fn)
> + if (iter_fn) {
> ret = do_iter_readv_writev(file, type, iov, nr_segs, tot_len,
> pos, iter_fn, flags);
> - else if (fnv)
> - ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
> - pos, fnv);
> - else
> - ret = do_loop_readv_writev(file, iov, nr_segs, pos, fn);
> + } else {
> + if (type == READ && (flags & RWF_NONBLOCK))
> + return -EAGAIN;
> +
> + if (fnv)
> + ret = do_sync_readv_writev(file, iov, nr_segs, tot_len,
> + pos, fnv);
> + else
> + ret = do_loop_readv_writev(file, iov, nr_segs, pos, fn);
> + }
>
> if (type != READ)
> file_end_write(file);
> @@ -866,8 +871,10 @@ ssize_t vfs_readv(struct file *file, const struct iovec __user *vec,
> return -EBADF;
> if (!(file->f_mode & FMODE_CAN_READ))
> return -EINVAL;
> - if (flags & ~0)
> + if (flags & ~RWF_NONBLOCK)
> return -EINVAL;
> + if ((file->f_flags & O_DIRECT) && (flags & RWF_NONBLOCK))
> + return -EAGAIN;
>
> return do_readv_writev(READ, file, vec, vlen, pos, flags);
> }
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index eb596b4..b1f6334 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -246,6 +246,10 @@ xfs_file_read_iter(
>
> XFS_STATS_INC(xs_read_calls);
>
> + /* XXX: need a non-blocking iolock helper, shouldn't be too hard */
> + if (iocb->ki_rwflags & RWF_NONBLOCK)
> + return -EAGAIN;
> +
> if (unlikely(file->f_flags & O_DIRECT))
> ioflags |= XFS_IO_ISDIRECT;
> if (file->f_mode & FMODE_NOCMTIME)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 9ed5711..eaebd99 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1459,6 +1459,9 @@ struct block_device_operations;
> #define HAVE_COMPAT_IOCTL 1
> #define HAVE_UNLOCKED_IOCTL 1
>
> +/* These flags are used for the readv/writev syscalls with flags. */
> +#define RWF_NONBLOCK 0x00000001
> +
> struct iov_iter;
>
> struct file_operations {
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 45964c8..e73ba7e 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1493,6 +1493,8 @@ static ssize_t do_generic_file_read(struct file *filp, loff_t *ppos,
> find_page:
> page = find_get_page(mapping, index);
> if (!page) {
> + if (flags & RWF_NONBLOCK)
> + goto would_block;
> page_cache_sync_readahead(mapping,
> ra, filp,
> index, last_index - index);
> @@ -1584,6 +1586,11 @@ page_ok:
> continue;
>
> page_not_up_to_date:
> + if (flags & RWF_NONBLOCK) {
> + page_cache_release(page);
> + goto would_block;
> + }
> +
> /* Get exclusive access to the page ... */
> error = lock_page_killable(page);
> if (unlikely(error))
> @@ -1603,6 +1610,12 @@ page_not_up_to_date_locked:
> goto page_ok;
> }
>
> + if (flags & RWF_NONBLOCK) {
> + unlock_page(page);
> + page_cache_release(page);
> + goto would_block;
> + }
> +
> readpage:
> /*
> * A previous I/O error may have been due to temporary
> @@ -1673,6 +1686,8 @@ no_cached_page:
> goto readpage;
> }
>
> +would_block:
> + error = -EAGAIN;
> out:
> ra->prev_pos = prev_index;
> ra->prev_pos <<= PAGE_CACHE_SHIFT;
> @@ -1706,6 +1721,9 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter)
> size_t count = iov_iter_count(iter);
> loff_t size;
>
> + if (iocb->ki_rwflags & RWF_NONBLOCK)
> + return -EAGAIN;
> +
> if (!count)
> goto out; /* skip atime */
> size = i_size_read(inode);
> diff --git a/mm/shmem.c b/mm/shmem.c
> index cd6fc75..5c30f04 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1531,6 +1531,10 @@ static ssize_t shmem_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> ssize_t retval = 0;
> loff_t *ppos = &iocb->ki_pos;
>
> + /* XXX: should be easily supportable */
> + if (iocb->ki_rwflags & RWF_NONBLOCK)
> + return -EAGAIN;
> +
> /*
> * Might this read be for a stacking filesystem? Then when reading
> * holes of a sparse file, we actually need to allocate those pages,
> --
> 1.9.1
>
> --
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--
Thanks,

Steve
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Next message: Kamal Mostafa: "[PATCH 3.13 073/105] ASoC: tlv320aic3x: fix PLL D configuration"
Previous message: Suravee Suthikulanit: "Re: [PATCH V2] arm64: amd-seattle: Adding device tree for AMD Seattle platform"
In reply to: Christoph Hellwig: "Re: [PATCH 4/4] vfs: RWF_NONBLOCK flag for preadv2"
Next in thread: Milosz Tanski: "Re: [PATCH 4/4] vfs: RWF_NONBLOCK flag for preadv2"
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