From: Ira Weiny <[email protected]>
Linux 5.8 is slated to have STATX_ATTR_DAX support.
https://lore.kernel.org/lkml/[email protected]/
https://lore.kernel.org/lkml/20200504161352.GA13783@magnolia/
Add the text to the statx man page.
Signed-off-by: Ira Weiny <[email protected]>
---
man2/statx.2 | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/man2/statx.2 b/man2/statx.2
index 2e90f07dbdbc..14c4ab78e7bd 100644
--- a/man2/statx.2
+++ b/man2/statx.2
@@ -468,6 +468,30 @@ The file has fs-verity enabled.
It cannot be written to, and all reads from it will be verified
against a cryptographic hash that covers the
entire file (e.g., via a Merkle tree).
+.TP
+.BR STATX_ATTR_DAX (since Linux 5.8)
+The file is in the DAX (cpu direct access) state. DAX state attempts to
+minimize software cache effects for both I/O and memory mappings of this file.
+It requires a file system which has been configured to support DAX.
+.PP
+DAX generally assumes all accesses are via cpu load / store instructions which
+can minimize overhead for small accesses, but may adversely affect cpu
+utilization for large transfers.
+.PP
+File I/O is done directly to/from user-space buffers and memory mapped I/O may
+be performed with direct memory mappings that bypass kernel page cache.
+.PP
+While the DAX property tends to result in data being transferred synchronously,
+it does not give the same guarantees of O_SYNC where data and the necessary
+metadata are transferred together.
+.PP
+A DAX file may support being mapped with the MAP_SYNC flag, which enables a
+program to use CPU cache flush instructions to persist CPU store operations
+without an explicit
+.BR fsync(2).
+See
+.BR mmap(2)
+for more information.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
--
2.25.1
On Tue, Sep 29, 2020 at 10:38:46AM +0200, Michael Kerrisk (man-pages) wrote:
> Hello Ira,
>
> On 9/28/20 6:42 PM, Ira Weiny wrote:
> > On Mon, May 04, 2020 at 05:20:16PM -0700, 'Ira Weiny' wrote:
> >> From: Ira Weiny <[email protected]>
> >>
> >> Linux 5.8 is slated to have STATX_ATTR_DAX support.
> >>
> >> https://lore.kernel.org/lkml/[email protected]/
> >> https://lore.kernel.org/lkml/20200504161352.GA13783@magnolia/
> >>
> >> Add the text to the statx man page.
> >>
> >> Signed-off-by: Ira Weiny <[email protected]>
> >
> > Have I sent this to the wrong list? Or perhaps I have missed a reply.
>
> No, it's just me being a bit slow, I'm sorry. Thank you for pining.
NP
>
> > I don't see this applied to the man-pages project.[1] But perhaps I am looking
> > at the wrong place?
>
> Your patch is applied now, and pushed to kernel .org. Thanks!
Sweet! Thank you!
Ira
>
> Cheers,
>
> Michael
>