From: Prasad Singamsetty <[email protected]>
Userspace may add flag RWF_ATOMIC to pwritev2() to indicate that the
write is to be issued with torn write prevention, according to special
alignment and length rules.
Torn write prevention means that for a power or any other HW failure, all
or none of the data will be committed to storage, but never a mix of old
and new.
For any syscall interface utilizing struct iocb, add IOCB_ATOMIC for
iocb->ki_flags field to indicate the same.
A call to statx will give the relevant atomic write info:
- atomic_write_unit_min
- atomic_write_unit_max
Both values are a power-of-2.
Applications can avail of atomic write feature by ensuring that the total
length of a write is a power-of-2 in size and also sized between
atomic_write_unit_min and atomic_write_unit_max, inclusive. Applications
must ensure that the write is at a naturally-aligned offset in the file
wrt the total write length.
Add file mode flag FMODE_CAN_ATOMIC_WRITE, so files which do not have the
flag set will have RWF_ATOMIC rejected and not just ignored.
Signed-off-by: Prasad Singamsetty <[email protected]>
Signed-off-by: John Garry <[email protected]>
---
include/linux/fs.h | 8 ++++++++
include/uapi/linux/fs.h | 5 ++++-
2 files changed, 12 insertions(+), 1 deletion(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 70329c81be31..d725c194243c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -185,6 +185,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/* File supports async nowait buffered writes */
#define FMODE_BUF_WASYNC ((__force fmode_t)0x80000000)
+/* File supports atomic writes */
+#define FMODE_CAN_ATOMIC_WRITE ((__force fmode_t)0x100000000)
+
/*
* Attribute flags. These should be or-ed together to figure out what
* has been changed!
@@ -328,6 +331,7 @@ enum rw_hint {
#define IOCB_SYNC (__force int) RWF_SYNC
#define IOCB_NOWAIT (__force int) RWF_NOWAIT
#define IOCB_APPEND (__force int) RWF_APPEND
+#define IOCB_ATOMIC (__force int) RWF_ATOMIC
/* non-RWF related bits - start at 16 */
#define IOCB_EVENTFD (1 << 16)
@@ -3265,6 +3269,10 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
return -EOPNOTSUPP;
kiocb_flags |= IOCB_NOIO;
}
+ if (flags & RWF_ATOMIC) {
+ if (!(ki->ki_filp->f_mode & FMODE_CAN_ATOMIC_WRITE))
+ return -EOPNOTSUPP;
+ }
kiocb_flags |= (__force int) (flags & RWF_SUPPORTED);
if (flags & RWF_SYNC)
kiocb_flags |= IOCB_DSYNC;
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index da43810b7485..1a5c68d31ef5 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -301,9 +301,12 @@ typedef int __bitwise __kernel_rwf_t;
/* per-IO O_APPEND */
#define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
+/* Atomic Write */
+#define RWF_ATOMIC ((__force __kernel_rwf_t)0x00000020)
+
/* mask of flags supported by the kernel */
#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
- RWF_APPEND)
+ RWF_APPEND | RWF_ATOMIC)
/* Pagemap ioctl */
#define PAGEMAP_SCAN _IOWR('f', 16, struct pm_scan_arg)
--
2.35.3
On Tue, Dec 12, 2023 at 11:08:33AM +0000, John Garry wrote:
> Add file mode flag FMODE_CAN_ATOMIC_WRITE, so files which do not have the
> flag set will have RWF_ATOMIC rejected and not just ignored.
>
> Signed-off-by: Prasad Singamsetty <[email protected]>
> Signed-off-by: John Garry <[email protected]>
> ---
> include/linux/fs.h | 8 ++++++++
> include/uapi/linux/fs.h | 5 ++++-
> 2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 70329c81be31..d725c194243c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -185,6 +185,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
> /* File supports async nowait buffered writes */
> #define FMODE_BUF_WASYNC ((__force fmode_t)0x80000000)
>
> +/* File supports atomic writes */
> +#define FMODE_CAN_ATOMIC_WRITE ((__force fmode_t)0x100000000)
Have you even tried to compile that on e.g. arm?
On 13/12/2023 13:31, Al Viro wrote:
>> Add file mode flag FMODE_CAN_ATOMIC_WRITE, so files which do not have the
>> flag set will have RWF_ATOMIC rejected and not just ignored.
>>
>> Signed-off-by: Prasad Singamsetty<[email protected]>
>> Signed-off-by: John Garry<[email protected]>
>> ---
>> include/linux/fs.h | 8 ++++++++
>> include/uapi/linux/fs.h | 5 ++++-
>> 2 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 70329c81be31..d725c194243c 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -185,6 +185,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
>> /* File supports async nowait buffered writes */
>> #define FMODE_BUF_WASYNC ((__force fmode_t)0x80000000)
>>
>> +/* File supports atomic writes */
>> +#define FMODE_CAN_ATOMIC_WRITE ((__force fmode_t)0x100000000)
> Have you even tried to compile that on e.g. arm?
i386 and now arm32, and no grumblings.
I think that the issue is that we only ever do a bitwise OR or test that
bit 33 for a 32b value, and it is a void operation and ignored.
However if I have file.f_mode = FMODE_CAN_ATOMIC_WRITE and compile for
arm32, then it complains.
On 12/12/2023 11:08, John Garry wrote:
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -301,9 +301,12 @@ typedef int __bitwise __kernel_rwf_t;
> /* per-IO O_APPEND */
> #define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
>
> +/* Atomic Write */
> +#define RWF_ATOMIC ((__force __kernel_rwf_t)0x00000020)
> +
vfs maintainers, due to
https://lore.kernel.org/linux-fsdevel/[email protected]/T/#t,
I now plan to change this value to 0x40.
Thanks,
John