| Message ID | 20171019125817.11580-19-jack@suse.cz |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | mmap.2: Add description of MAP_SHARED_VALIDATE and MAP_SYNC | expand |
On Thu, Oct 19, 2017 at 02:58:17PM +0200, Jan Kara wrote: > Signed-off-by: Jan Kara <jack@suse.cz> > --- > 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 Some small nits: I think you should maybe include a "(since Linux 4.15)" type note after the MAP_SHARED_VALIDATE header. You also need to update the following line: Both of these flags are described in POSIX.1-2001 and POSIX.1-2008. Which used to refer to MAP_SYNC and MAP_PRIVATE.
On Fri 20-10-17 15:47:53, Ross Zwisler wrote: > On Thu, Oct 19, 2017 at 02:58:17PM +0200, Jan Kara wrote: > > Signed-off-by: Jan Kara <jack@suse.cz> > > --- > > 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 > > Some small nits: > > I think you should maybe include a "(since Linux 4.15)" type note after the > MAP_SHARED_VALIDATE header. You also need to update the following line: > > Both of these flags are described in POSIX.1-2001 and POSIX.1-2008. > > Which used to refer to MAP_SYNC and MAP_PRIVATE. Thanks, I've fixed these. Honza
On Tue, Oct 24, 2017 at 03:27:13PM +0200, Jan Kara wrote: > On Fri 20-10-17 15:47:53, Ross Zwisler wrote: > > On Thu, Oct 19, 2017 at 02:58:17PM +0200, Jan Kara wrote: > > > Signed-off-by: Jan Kara <jack@suse.cz> > > > --- > > > 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 > > > > Some small nits: > > > > I think you should maybe include a "(since Linux 4.15)" type note after the > > MAP_SHARED_VALIDATE header. You also need to update the following line: > > > > Both of these flags are described in POSIX.1-2001 and POSIX.1-2008. > > > > Which used to refer to MAP_SYNC and MAP_PRIVATE. > > Thanks, I've fixed these. Cool, you can add my: Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
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
Signed-off-by: Jan Kara <jack@suse.cz> --- man2/mmap.2 | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)