|
 |
18553a |
From d06094d4469258a722c94f8bb5bc25b5c9711718 Mon Sep 17 00:00:00 2001
|
|
|
18553a |
From: =?UTF-8?q?Nikola=20Forr=C3=B3?= <nforro@redhat.com>
|
|
|
18553a |
Date: Fri, 9 Jul 2021 18:34:34 +0200
|
|
|
18553a |
Subject: [PATCH 1/2] statx.2: add STATX_ATTR_DAX
|
|
|
18553a |
|
|
|
18553a |
---
|
|
|
18553a |
man-pages/man2/statx.2 | 30 ++++++++++++++++++++++++++++++
|
|
|
18553a |
1 file changed, 30 insertions(+)
|
|
|
18553a |
|
|
|
18553a |
diff --git a/man-pages/man2/statx.2 b/man-pages/man2/statx.2
|
|
|
18553a |
index bb04455..686edc8 100644
|
|
|
18553a |
--- a/man-pages/man2/statx.2
|
|
|
18553a |
+++ b/man-pages/man2/statx.2
|
|
|
18553a |
@@ -462,6 +462,36 @@ See
|
|
|
18553a |
.TP
|
|
|
18553a |
.B STATX_ATTR_ENCRYPTED
|
|
|
18553a |
A key is required for the file to be encrypted by the filesystem.
|
|
|
18553a |
+.TP
|
|
|
18553a |
+.BR STATX_ATTR_DAX " (since Linux 5.8)"
|
|
|
18553a |
+The file is in the DAX (cpu direct access) state.
|
|
|
18553a |
+DAX state attempts to
|
|
|
18553a |
+minimize software cache effects for both I/O and memory mappings of this file.
|
|
|
18553a |
+It requires a file system which has been configured to support DAX.
|
|
|
18553a |
+.IP
|
|
|
18553a |
+DAX generally assumes all accesses are via CPU load / store instructions
|
|
|
18553a |
+which can minimize overhead for small accesses,
|
|
|
18553a |
+but may adversely affect CPU utilization for large transfers.
|
|
|
18553a |
+.IP
|
|
|
18553a |
+File I/O is done directly to/from user-space buffers and memory mapped I/O may
|
|
|
18553a |
+be performed with direct memory mappings that bypass the kernel page cache.
|
|
|
18553a |
+.IP
|
|
|
18553a |
+While the DAX property tends to result in data being transferred synchronously,
|
|
|
18553a |
+it does not give the same guarantees as the
|
|
|
18553a |
+.B O_SYNC
|
|
|
18553a |
+flag (see
|
|
|
18553a |
+.BR open (2)),
|
|
|
18553a |
+where data and the necessary metadata are transferred together.
|
|
|
18553a |
+.IP
|
|
|
18553a |
+A DAX file may support being mapped with the
|
|
|
18553a |
+.B MAP_SYNC
|
|
|
18553a |
+flag, which enables a
|
|
|
18553a |
+program to use CPU cache flush instructions to persist CPU store operations
|
|
|
18553a |
+without an explicit
|
|
|
18553a |
+.BR fsync (2).
|
|
|
18553a |
+See
|
|
|
18553a |
+.BR mmap (2)
|
|
|
18553a |
+for more information.
|
|
|
18553a |
.SH RETURN VALUE
|
|
|
18553a |
On success, zero is returned.
|
|
|
18553a |
On error, \-1 is returned, and
|
|
|
18553a |
--
|
|
|
18553a |
2.31.1
|
|
|
18553a |
|