From: Jens Axboe <axboe@kernel.dk>
To: linux-man <linux-man@vger.kernel.org>
Cc: Michael Kerrisk-manpages <mtk.manpages@gmail.com>
Subject: [PATCH] man2/openat2.2: add RESOLVE_CACHED
Date: Thu, 17 Dec 2020 14:18:13 -0700 [thread overview]
Message-ID: <187e84bd-59c8-dc68-1eef-9cd13aa70d38@kernel.dk> (raw)
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>
---
First attempt at this, fully expecting the phrasing to require some
massaging.
Also see: https://lore.kernel.org/linux-fsdevel/20201217161911.743222-1-axboe@kernel.dk/T/
diff --git a/man2/openat2.2 b/man2/openat2.2
index 3bda20620574..282c13e2df96 100644
--- a/man2/openat2.2
+++ b/man2/openat2.2
@@ -385,6 +385,15 @@ 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
+Fail path resolution, unless all components needed already exist in the
+lookup cache. If any kind of revalidation or IO is needed to satisfy the
+lookup, then fail the open attempt with
+.B EAGAIN.
+This is useful in providing a fast path open that can be performed without
+resorting to thread offload, or other mechanism that an application might
+use to offload slower operations.
.RE
.IP
If any bits other than those listed above are set in
@@ -421,6 +430,14 @@ 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 cached. 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
next reply other threads:[~2020-12-17 21:19 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-17 21:18 Jens Axboe [this message]
2020-12-23 12:41 ` [PATCH] man2/openat2.2: add RESOLVE_CACHED Michael Kerrisk (man-pages)
2020-12-23 14:04 ` Jens Axboe
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