mmap.2: Add description of MAP_SHARED_VALIDATE and MAP_SYNC

Message ID 20171024152415.22864-19-jack@suse.cz
State New
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Series
  • mmap.2: Add description of MAP_SHARED_VALIDATE and MAP_SYNC
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Commit Message

Jan Kara Oct. 24, 2017, 3:24 p.m.
Signed-off-by: Jan Kara <jack@suse.cz>
---
 man2/mmap.2 | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

Comments

Ross Zwisler Oct. 24, 2017, 9:10 p.m. | #1
On Tue, Oct 24, 2017 at 05:24:15PM +0200, Jan Kara wrote:
> Signed-off-by: Jan Kara <jack@suse.cz>

This looks unchanged since the previous version?

> ---
>  man2/mmap.2 | 30 ++++++++++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/man2/mmap.2 b/man2/mmap.2
> index 47c3148653be..598ff0c64f7f 100644
> --- a/man2/mmap.2
> +++ b/man2/mmap.2
> @@ -125,6 +125,21 @@ are carried through to the underlying file.
>  to the underlying file requires the use of
>  .BR msync (2).)
>  .TP
> +.B MAP_SHARED_VALIDATE
> +The same as
> +.B MAP_SHARED
> +except that
> +.B MAP_SHARED
> +mappings ignore unknown flags in
> +.IR flags .
> +In contrast when creating mapping of
> +.B MAP_SHARED_VALIDATE
> +mapping type, the kernel verifies all passed flags are known and fails the
> +mapping with
> +.BR EOPNOTSUPP
> +otherwise. This mapping type is also required to be able to use some mapping
> +flags.
> +.TP
>  .B MAP_PRIVATE
>  Create a private copy-on-write mapping.
>  Updates to the mapping are not visible to other processes
> @@ -352,6 +367,21 @@ option.
>  Because of the security implications,
>  that option is normally enabled only on embedded devices
>  (i.e., devices where one has complete control of the contents of user memory).
> +.TP
> +.BR MAP_SYNC " (since Linux 4.15)"
> +This flags is available only with
> +.B MAP_SHARED_VALIDATE
> +mapping type. Mappings of
> +.B MAP_SHARED
> +type will silently ignore this flag.
> +This flag is supported only for files supporting DAX (direct mapping of persistent
> +memory). For other files, creating mapping with this flag results in
> +.B EOPNOTSUPP
> +error. Shared file mappings with this flag provide the guarantee that while
> +some memory is writeably mapped in the address space of the process, it will
> +be visible in the same file at the same offset even after the system crashes or
> +is rebooted. This allows users of such mappings to make data modifications
> +persistent in a more efficient way using appropriate CPU instructions.
>  .PP
>  Of the above flags, only
>  .B MAP_FIXED
> -- 
> 2.12.3
>
Jan Kara Oct. 26, 2017, 1:24 p.m. | #2
On Tue 24-10-17 15:10:07, Ross Zwisler wrote:
> On Tue, Oct 24, 2017 at 05:24:15PM +0200, Jan Kara wrote:
> > Signed-off-by: Jan Kara <jack@suse.cz>
> 
> This looks unchanged since the previous version?

Ah, thanks for checking. I forgot to commit modifications. Attached is
really updated patch.

								Honza
Ross Zwisler Oct. 26, 2017, 6:22 p.m. | #3
On Thu, Oct 26, 2017 at 03:24:02PM +0200, Jan Kara wrote:
> On Tue 24-10-17 15:10:07, Ross Zwisler wrote:
> > On Tue, Oct 24, 2017 at 05:24:15PM +0200, Jan Kara wrote:
> > > Signed-off-by: Jan Kara <jack@suse.cz>
> > 
> > This looks unchanged since the previous version?
> 
> Ah, thanks for checking. I forgot to commit modifications. Attached is
> really updated patch.
> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR

> From 59eeec2998ed9b3840aab951f213148cb1d053a5 Mon Sep 17 00:00:00 2001
> From: Jan Kara <jack@suse.cz>
> Date: Thu, 19 Oct 2017 14:44:55 +0200
> Subject: [PATCH] mmap.2: Add description of MAP_SHARED_VALIDATE and MAP_SYNC
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Looks good, you can add: 

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>

Patch

diff --git a/man2/mmap.2 b/man2/mmap.2
index 47c3148653be..598ff0c64f7f 100644
--- a/man2/mmap.2
+++ b/man2/mmap.2
@@ -125,6 +125,21 @@  are carried through to the underlying file.
 to the underlying file requires the use of
 .BR msync (2).)
 .TP
+.B MAP_SHARED_VALIDATE
+The same as
+.B MAP_SHARED
+except that
+.B MAP_SHARED
+mappings ignore unknown flags in
+.IR flags .
+In contrast when creating mapping of
+.B MAP_SHARED_VALIDATE
+mapping type, the kernel verifies all passed flags are known and fails the
+mapping with
+.BR EOPNOTSUPP
+otherwise. This mapping type is also required to be able to use some mapping
+flags.
+.TP
 .B MAP_PRIVATE
 Create a private copy-on-write mapping.
 Updates to the mapping are not visible to other processes
@@ -352,6 +367,21 @@  option.
 Because of the security implications,
 that option is normally enabled only on embedded devices
 (i.e., devices where one has complete control of the contents of user memory).
+.TP
+.BR MAP_SYNC " (since Linux 4.15)"
+This flags is available only with
+.B MAP_SHARED_VALIDATE
+mapping type. Mappings of
+.B MAP_SHARED
+type will silently ignore this flag.
+This flag is supported only for files supporting DAX (direct mapping of persistent
+memory). For other files, creating mapping with this flag results in
+.B EOPNOTSUPP
+error. Shared file mappings with this flag provide the guarantee that while
+some memory is writeably mapped in the address space of the process, it will
+be visible in the same file at the same offset even after the system crashes or
+is rebooted. This allows users of such mappings to make data modifications
+persistent in a more efficient way using appropriate CPU instructions.
 .PP
 Of the above flags, only
 .B MAP_FIXED