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