2017-09-29 12:07:57

by Jürg Billeter

Subject: [RESEND PATCH] fs: add RWF_APPEND

This is the per-I/O equivalent of O_APPEND to support atomic append
operations on any open file.

If a file is opened with O_APPEND, pwrite() ignores the offset and
always appends data to the end of the file. RWF_APPEND enables atomic
append and pwrite() with offset on a single file descriptor.

Signed-off-by: Jürg Billeter <[email protected]>
---
include/linux/fs.h | 2 ++
include/uapi/linux/fs.h | 6 +++++-
2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 339e73742e73..fee24eae7523 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3204,6 +3204,8 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
ki->ki_flags |= IOCB_DSYNC;
if (flags & RWF_SYNC)
ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
+ if (flags & RWF_APPEND)
+ ki->ki_flags |= IOCB_APPEND;
return 0;
}

diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 56235dddea7d..ac145430bcd8 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -376,7 +376,11 @@ typedef int __bitwise __kernel_rwf_t;
/* per-IO, return -EAGAIN if operation would block */
#define RWF_NOWAIT ((__force __kernel_rwf_t)0x00000008)

+/* per-IO O_APPEND */
+#define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
+
/* mask of flags supported by the kernel */
-#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT)
+#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
+ RWF_APPEND)

#endif /* _UAPI_LINUX_FS_H */
--
2.14.1

2017-10-01 00:32:05

by Goldwyn Rodrigues

Subject: Re: [RESEND PATCH] fs: add RWF_APPEND

On 09/29/2017 07:07 AM, Jürg Billeter wrote:
> This is the per-I/O equivalent of O_APPEND to support atomic append
> operations on any open file.
>
> If a file is opened with O_APPEND, pwrite() ignores the offset and
> always appends data to the end of the file. RWF_APPEND enables atomic
> append and pwrite() with offset on a single file descriptor.
>

I think similarly we can introduce RWF_DIRECT, though I am not sure if
users would want to mix buffered writes and direct writes.

Reviewed-by: Goldwyn Rodrigues <[email protected]>

> Signed-off-by: Jürg Billeter <[email protected]>
> ---
> include/linux/fs.h | 2 ++
> include/uapi/linux/fs.h | 6 +++++-
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 339e73742e73..fee24eae7523 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -3204,6 +3204,8 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
> ki->ki_flags |= IOCB_DSYNC;
> if (flags & RWF_SYNC)
> ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
> + if (flags & RWF_APPEND)
> + ki->ki_flags |= IOCB_APPEND;
> return 0;
> }
>
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 56235dddea7d..ac145430bcd8 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -376,7 +376,11 @@ typedef int __bitwise __kernel_rwf_t;
> /* per-IO, return -EAGAIN if operation would block */
> #define RWF_NOWAIT ((__force __kernel_rwf_t)0x00000008)
>
> +/* per-IO O_APPEND */
> +#define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
> +
> /* mask of flags supported by the kernel */
> -#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT)
> +#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
> + RWF_APPEND)
>
> #endif /* _UAPI_LINUX_FS_H */
>

--
Goldwyn