* [PATCH v3] man2/openat2.2: add RESOLVE_CACHED
@ 2021-02-21 13:12 Jens Axboe
2021-02-22 20:01 ` Michael Kerrisk (man-pages)
0 siblings, 1 reply; 4+ messages in thread
From: Jens Axboe @ 2021-02-21 13:12 UTC (permalink / raw
To: linux-man, Michael Kerrisk-manpages
RESOLVE_CACHED allows an application to attempt a cache-only open
of a file. If this isn't possible, the request will fail with
-1/EAGAIN and the caller should retry without RESOLVE_CACHED set.
This will generally happen from a different context, where a slower
open operation can be performed.
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
Since v2:
- Incorporate suggested edits from Michael
diff --git a/man2/openat2.2 b/man2/openat2.2
index 3bda20620574..a8381c753f0d 100644
--- a/man2/openat2.2
+++ b/man2/openat2.2
@@ -385,6 +385,17 @@ This may occur if, for example,
a system pathname that is used by an application is modified
(e.g., in a new distribution release)
so that a pathname component (now) contains a bind mount.
+.TP
+.B RESOLVE_CACHED
+Make the open operation fail unless all path components are already present
+in the kernel's lookup cache.
+If any kind of revalidation or I/O is needed to satisfy the lookup,
+.BR openat2 ()
+fails with the error
+.B EAGAIN .
+This is useful in providing a fast-path open that can be performed without
+resorting to thread offload, or other mechanisms that an application might
+use to offload slower operations.
.RE
.IP
If any bits other than those listed above are set in
@@ -421,6 +432,14 @@ The caller may choose to retry the
.BR openat2 ()
call.
.TP
+.B EAGAIN
+.BR RESOLVE_CACHED
+was set, and the open operation cannot be performed using only cached
+information. The caller should retry without
+.B RESOLVE_CACHED
+set in
+.I how.resolve .
+.TP
.B EINVAL
An unknown flag or invalid value was specified in
.IR how .
--
Jens Axboe
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v3] man2/openat2.2: add RESOLVE_CACHED
2021-02-21 13:12 [PATCH v3] man2/openat2.2: add RESOLVE_CACHED Jens Axboe
@ 2021-02-22 20:01 ` Michael Kerrisk (man-pages)
2021-02-22 20:05 ` Jens Axboe
0 siblings, 1 reply; 4+ messages in thread
From: Michael Kerrisk (man-pages) @ 2021-02-22 20:01 UTC (permalink / raw
To: Jens Axboe, linux-man; +Cc: mtk.manpages
Hi Jens,
On 2/21/21 2:12 PM, Jens Axboe wrote:
> RESOLVE_CACHED allows an application to attempt a cache-only open
> of a file. If this isn't possible, the request will fail with
> -1/EAGAIN and the caller should retry without RESOLVE_CACHED set.
> This will generally happen from a different context, where a slower
> open operation can be performed.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Is it correct that this feature is now merged?
Cheers,
Michael
>
> ---
>
> Since v2:
> - Incorporate suggested edits from Michael
>
> diff --git a/man2/openat2.2 b/man2/openat2.2
> index 3bda20620574..a8381c753f0d 100644
> --- a/man2/openat2.2
> +++ b/man2/openat2.2
> @@ -385,6 +385,17 @@ This may occur if, for example,
> a system pathname that is used by an application is modified
> (e.g., in a new distribution release)
> so that a pathname component (now) contains a bind mount.
> +.TP
> +.B RESOLVE_CACHED
> +Make the open operation fail unless all path components are already present
> +in the kernel's lookup cache.
> +If any kind of revalidation or I/O is needed to satisfy the lookup,
> +.BR openat2 ()
> +fails with the error
> +.B EAGAIN .
> +This is useful in providing a fast-path open that can be performed without
> +resorting to thread offload, or other mechanisms that an application might
> +use to offload slower operations.
> .RE
> .IP
> If any bits other than those listed above are set in
> @@ -421,6 +432,14 @@ The caller may choose to retry the
> .BR openat2 ()
> call.
> .TP
> +.B EAGAIN
> +.BR RESOLVE_CACHED
> +was set, and the open operation cannot be performed using only cached
> +information. The caller should retry without
> +.B RESOLVE_CACHED
> +set in
> +.I how.resolve .
> +.TP
> .B EINVAL
> An unknown flag or invalid value was specified in
> .IR how .
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v3] man2/openat2.2: add RESOLVE_CACHED
2021-02-22 20:01 ` Michael Kerrisk (man-pages)
@ 2021-02-22 20:05 ` Jens Axboe
2021-03-03 21:09 ` Michael Kerrisk (man-pages)
0 siblings, 1 reply; 4+ messages in thread
From: Jens Axboe @ 2021-02-22 20:05 UTC (permalink / raw
To: Michael Kerrisk (man-pages), linux-man
On 2/22/21 1:01 PM, Michael Kerrisk (man-pages) wrote:
> Hi Jens,
>
> On 2/21/21 2:12 PM, Jens Axboe wrote:
>> RESOLVE_CACHED allows an application to attempt a cache-only open
>> of a file. If this isn't possible, the request will fail with
>> -1/EAGAIN and the caller should retry without RESOLVE_CACHED set.
>> This will generally happen from a different context, where a slower
>> open operation can be performed.
>>
>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>
> Is it correct that this feature is now merged?
Yes, it's in Linus's tree:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs/open.c?id=99668f618062816ca7ba639b007eb145b9d3d41e
--
Jens Axboe
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v3] man2/openat2.2: add RESOLVE_CACHED
2021-02-22 20:05 ` Jens Axboe
@ 2021-03-03 21:09 ` Michael Kerrisk (man-pages)
0 siblings, 0 replies; 4+ messages in thread
From: Michael Kerrisk (man-pages) @ 2021-03-03 21:09 UTC (permalink / raw
To: Jens Axboe, linux-man; +Cc: mtk.manpages
Hi Jens,
On 2/22/21 9:05 PM, Jens Axboe wrote:
> On 2/22/21 1:01 PM, Michael Kerrisk (man-pages) wrote:
>> Hi Jens,
>>
>> On 2/21/21 2:12 PM, Jens Axboe wrote:
>>> RESOLVE_CACHED allows an application to attempt a cache-only open
>>> of a file. If this isn't possible, the request will fail with
>>> -1/EAGAIN and the caller should retry without RESOLVE_CACHED set.
>>> This will generally happen from a different context, where a slower
>>> open operation can be performed.
>>>
>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
>>
>> Is it correct that this feature is now merged?
>
> Yes, it's in Linus's tree:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/fs/open.c?id=99668f618062816ca7ba639b007eb145b9d3d41e
Thanks. Patch applied.
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
^ permalink raw reply [flat|nested] 4+ messages in thread
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-- links below jump to the message on this page --
2021-02-21 13:12 [PATCH v3] man2/openat2.2: add RESOLVE_CACHED Jens Axboe
2021-02-22 20:01 ` Michael Kerrisk (man-pages)
2021-02-22 20:05 ` Jens Axboe
2021-03-03 21:09 ` Michael Kerrisk (man-pages)
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