fs: Introduce RWF_NOWAIT and FMODE_AIO_NOWAIT

RWF_NOWAIT 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.

RWF_NOWAIT is translated to IOCB_NOWAIT for iocb->ki_flags.

FMODE_AIO_NOWAIT is a flag which identifies the file opened is capable
of returning -EAGAIN if the AIO call will block. This must be set by
supporting filesystems in the ->open() call.

Filesystems xfs, btrfs and ext4 would be supported in the following patches.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/aio.c b/fs/aio.c
index 020fa0045e3c154762bf8d896d1b562305406401..34027b67e2f4bc42be8f6126956b7d07d3937f0f 100644 (file)
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1592,6 +1592,12 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
                goto out_put_req;
        }
 
+       if ((req->common.ki_flags & IOCB_NOWAIT) &&
+                       !(req->common.ki_flags & IOCB_DIRECT)) {
+               ret = -EOPNOTSUPP;
+               goto out_put_req;
+       }
+
        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 0d34f5b5a6b065ab38c6bf1dd4176dfa1d3e18d7..4574121f4746c062e90a1e27737ad55c5faa1ada 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -143,6 +143,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 /* File was opened by fanotify and shouldn't generate fanotify events */
 #define FMODE_NONOTIFY         ((__force fmode_t)0x4000000)
 
+/* File is capable of returning -EAGAIN if AIO will block */
+#define FMODE_AIO_NOWAIT       ((__force fmode_t)0x8000000)
+
 /*
  * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
  * that indicates that they should check the contents of the iovec are
@@ -269,6 +272,7 @@ 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;
@@ -3064,6 +3068,11 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, int flags)
        if (unlikely(flags & ~RWF_SUPPORTED))
                return -EOPNOTSUPP;
 
+       if (flags & RWF_NOWAIT) {
+               if (!(ki->ki_filp->f_mode & FMODE_AIO_NOWAIT))
+                       return -EOPNOTSUPP;
+               ki->ki_flags |= IOCB_NOWAIT;
+       }
        if (flags & RWF_HIPRI)
                ki->ki_flags |= IOCB_HIPRI;
        if (flags & RWF_DSYNC)

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 937c3e39650a0ae3eefd422dba7a677e4646f486..27d8c36c04af89a29ea42c6b84f3602af3dd27ed 100644 (file)
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -360,7 +360,9 @@ struct fscrypt_key {
 #define RWF_HIPRI                      0x00000001 /* high priority request, poll if possible */
 #define RWF_DSYNC                      0x00000002 /* per-IO O_DSYNC */
 #define RWF_SYNC                       0x00000004 /* per-IO O_SYNC */
+#define RWF_NOWAIT                     0x00000008 /* per-IO, return -EAGAIN if operation would block */
 
-#define RWF_SUPPORTED                  (RWF_HIPRI | RWF_DSYNC | RWF_SYNC)
+#define RWF_SUPPORTED                  (RWF_HIPRI | RWF_DSYNC | RWF_SYNC |\
+                                        RWF_NOWAIT)
 
 #endif /* _UAPI_LINUX_FS_H */