From: Goldwyn Rodrigues <rgoldwyn-IBi9RG/[email protected]>
This flag informs kernel to bail out if an AIO request will block
for reasons such as file allocations, or a writeback triggered,
or would block while allocating requests while performing
direct I/O.
Unfortunately, aio_flags is not checked for validity, which would
break existing applications which have it set to anything besides zero
or IOCB_FLAG_RESFD. So, we are using aio_reserved1 and renaming it
to aio_rw_flags.
IOCB_RW_FLAG_NOWAIT is translated to IOCB_NOWAIT for
iocb->ki_flags.
Added FS_NOWAIT to make sure VFS knows that the filesystem is capable
of performing direct-AIO with IOCB_RW_FLAG_NOWAIT.
---
fs/aio.c | 15 ++++++++++++++-
include/linux/fs.h | 2 ++
include/uapi/linux/aio_abi.h | 9 ++++++++-
3 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index f52d925..25ae59b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1541,11 +1541,16 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
ssize_t ret;
/* enforce forwards compatibility on users */
- if (unlikely(iocb->aio_reserved1 || iocb->aio_reserved2)) {
+ if (unlikely(iocb->aio_reserved2)) {
pr_debug("EINVAL: reserve field set\n");
return -EINVAL;
}
+ if (unlikely(iocb->aio_rw_flags & ~IOCB_RW_FLAG_NOWAIT)) {
+ pr_debug("EINVAL: aio_rw_flags set with incompatible flags\n");
+ return -EINVAL;
+ }
+
/* prevent overflows */
if (unlikely(
(iocb->aio_buf != (unsigned long)iocb->aio_buf) ||
@@ -1586,6 +1591,14 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
req->common.ki_flags |= IOCB_EVENTFD;
}
+ if (iocb->aio_rw_flags & IOCB_RW_FLAG_NOWAIT) {
+ if (!(file->f_inode->i_sb->s_type->fs_flags & FS_NOWAIT)) {
+ ret = -EOPNOTSUPP;
+ goto out_put_req;
+ }
+ req->common.ki_flags |= IOCB_NOWAIT;
+ }
+
ret = put_user(KIOCB_KEY, &user_iocb->aio_key);
if (unlikely(ret)) {
pr_debug("EFAULT: aio_key\n");
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 7251f7b..802cfe2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -270,6 +270,7 @@ struct writeback_control;
#define IOCB_DSYNC (1 << 4)
#define IOCB_SYNC (1 << 5)
#define IOCB_WRITE (1 << 6)
+#define IOCB_NOWAIT (1 << 7)
struct kiocb {
struct file *ki_filp;
@@ -2020,6 +2021,7 @@ struct file_system_type {
#define FS_HAS_SUBTYPE 4
#define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */
+#define FS_NOWAIT 65536 /* FS supports nowait direct AIO */
struct dentry *(*mount) (struct file_system_type *, int,
const char *, void *);
void (*kill_sb) (struct super_block *);
diff --git a/include/uapi/linux/aio_abi.h b/include/uapi/linux/aio_abi.h
index bb2554f..6d98cbe 100644
--- a/include/uapi/linux/aio_abi.h
+++ b/include/uapi/linux/aio_abi.h
@@ -54,6 +54,13 @@ enum {
*/
#define IOCB_FLAG_RESFD (1 << 0)
+/*
+ * Flags for aio_rw_flags member of "struct iocb".
+ * IOCB_RW_FLAG_NOWAIT - Set if the user wants the iocb to fail if it
+ * would block for operations such as disk allocation.
+ */
+#define IOCB_RW_FLAG_NOWAIT (1 << 1)
+
/* read() from /dev/aio returns these structures. */
struct io_event {
__u64 data; /* the data field from the iocb */
@@ -79,7 +86,7 @@ struct io_event {
struct iocb {
/* these are internal to the kernel/libc. */
__u64 aio_data; /* data to be returned in event's data */
- __u32 PADDED(aio_key, aio_reserved1);
+ __u32 PADDED(aio_key, aio_rw_flags);
/* the kernel sets aio_key to the req # */
/* common fields */
--
2.10.2
On Mon, Apr 03, 2017 at 01:53:00PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <[email protected]>
>
> This flag informs kernel to bail out if an AIO request will block
> for reasons such as file allocations, or a writeback triggered,
> or would block while allocating requests while performing
> direct I/O.
>
> Unfortunately, aio_flags is not checked for validity, which would
> break existing applications which have it set to anything besides zero
> or IOCB_FLAG_RESFD. So, we are using aio_reserved1 and renaming it
> to aio_rw_flags.
>
> IOCB_RW_FLAG_NOWAIT is translated to IOCB_NOWAIT for
> iocb->ki_flags.
Please make this a flag in the RWF_* namespace, and as a preparation
support the existing RWF_* flags for aio.