[PATCH v7 4/5] vfs: RWF_NONBLOCK flag for preadv2

Milosz Tanski
2015-03-16T18:27:59Z

generic_file_read_iter() supports a new flag RWF_NONBLOCK which says that we
only want to read the data if it's already in the page cache.

Additionally, there are a few filesystems that we have to specifically
bail early if RWF_NONBLOCK because the op would block. Christoph Hellwig
contributed this code.

Signed-off-by: Milosz Tanski <milosz@adfin.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Acked-by: Sage Weil <sage@redhat.com>
---
fs/ceph/file.c | 2 ++
fs/cifs/file.c | 6 ++++++
fs/nfs/file.c | 5 ++++-
fs/ocfs2/file.c | 6 ++++++
fs/pipe.c | 3 ++-
fs/read_write.c | 44 ++++++++++++++++++++++++++++++--------------
fs/xfs/xfs_file.c | 4 ++++
include/linux/fs.h | 2 ++
mm/filemap.c | 18 ++++++++++++++++++
mm/shmem.c | 4 ++++
10 files changed, 78 insertions(+), 16 deletions(-)

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index d533075..78bdde3 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -831,6 +831,8 @@ again:
if ((got & (CEPH_CAP_FILE_CACHE|CEPH_CAP_FILE_LAZYIO)) == 0 ||
(iocb->ki_filp->f_flags & O_DIRECT) ||
(fi->flags & CEPH_F_SYNC)) {
+ if (iocb->ki_rwflags & O_NONBLOCK)
+ return -EAGAIN;

dout("aio_sync_read %p %llx.%llx %llu~%u got cap refs on %s\n",
inode, ceph_vinop(inode), iocb->ki_pos, (unsigned)len,
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index a94b3e6..1d16b5a 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -3003,6 +3003,9 @@ 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;
@@ -3121,6 +3124,9 @@ 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/nfs/file.c b/fs/nfs/file.c
index e679d24..58c21d7 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -171,8 +171,11 @@ nfs_file_read(struct kiocb *iocb, struct iov_iter *to)
struct inode *inode = file_inode(iocb->ki_filp);
ssize_t result;

- if (iocb->ki_filp->f_flags & O_DIRECT)
+ if (iocb->ki_filp->f_flags & O_DIRECT) {
+ if (iocb->ki_rwflags & O_NONBLOCK)
+ return -EAGAIN;
return nfs_file_direct_read(iocb, to, iocb->ki_pos);
+ }

dprintk("NFS: read(%pD2, %zu@%lu)\n",
iocb->ki_filp,
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 46e0d4e..c155752 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2536,6 +2536,12 @@ 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 e91f46e..339477b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -893,14 +893,19 @@ 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);
@@ -924,8 +929,10 @@ 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);
}
@@ -1127,14 +1134,19 @@ static ssize_t compat_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);
@@ -1163,7 +1175,11 @@ static size_t compat_readv(struct file *file,
ret = -EINVAL;
if (!(file->f_mode & FMODE_CAN_READ))
goto out;
- if (flags & ~0)
+ if (flags & ~RWF_NONBLOCK)
+ goto out;
+
+ ret = -EAGAIN;
+ if ((file->f_flags & O_DIRECT) && (flags & RWF_NONBLOCK))
goto out;

ret = compat_do_readv_writev(READ, file, vec, vlen, pos, flags);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index a2e1cb8..a38ddc1 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -280,6 +280,10 @@ 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 c018335..fb2de58 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1531,6 +1531,8 @@ struct block_device_operations;
#define NOMMU_VMFLAGS \
(NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC)

+/* These flags are used for the readv/writev syscalls with flags. */
+#define RWF_NONBLOCK 0x00000001

struct iov_iter;

diff --git a/mm/filemap.c b/mm/filemap.c
index 7865f64..ad789e0 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1490,6 +1490,8 @@ 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);
@@ -1581,6 +1583,11 @@ 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))
@@ -1600,6 +1607,12 @@ 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
@@ -1670,6 +1683,8 @@ no_cached_page:
goto readpage;
}

+would_block:
+ error = -EAGAIN;
out:
ra->prev_pos = prev_index;
ra->prev_pos <<= PAGE_CACHE_SHIFT;
@@ -1702,6 +1717,9 @@ 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 cf2d0ca..c5b78f8 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1528,6 +1528,10 @@ 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