| Message ID | 20171101153648.30166-20-jack@suse.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hello Jan, I have applied your patch, and tweaked the text a little, and pushed the result to the git repo. On 1 November 2017 at 16:36, Jan Kara <jack@suse.cz> wrote: > Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> > Signed-off-by: Jan Kara <jack@suse.cz> I have a question below. > --- > man2/mmap.2 | 35 ++++++++++++++++++++++++++++++++++- > 1 file changed, 34 insertions(+), 1 deletion(-) > > diff --git a/man2/mmap.2 b/man2/mmap.2 > index 47c3148653be..b38ee6809327 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 > +.BR MAP_SHARED_VALIDATE " (since Linux 4.15)" > +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 > @@ -134,7 +149,10 @@ It is unspecified whether changes made to the file after the > .BR mmap () > call are visible in the mapped region. > .PP > -Both of these flags are described in POSIX.1-2001 and POSIX.1-2008. > +.B MAP_SHARED > +and > +.B MAP_PRIVATE > +are described in POSIX.1-2001 and POSIX.1-2008. > .PP > In addition, zero or more of the following values can be ORed in > .IR flags : > @@ -352,6 +370,21 @@ 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. It feels like there's a word missing/unclear wording in the previous line, before "using". Without that word, the sentence feels a bit ambiguous. Should it be: persistent in a more efficient way *through the use of* appropriate CPU instructions. or: persistent in a more efficient way *than using* appropriate CPU instructions. ? Is suspect the first is correct, but need to check. Cheers, Michael
On Thu, Apr 12, 2018 at 03:00:49PM +0200, Michael Kerrisk (man-pages) wrote: > Hello Jan, > > I have applied your patch, and tweaked the text a little, and pushed > the result to the git repo. > > On 1 November 2017 at 16:36, Jan Kara <jack@suse.cz> wrote: > > Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> > > Signed-off-by: Jan Kara <jack@suse.cz> > > I have a question below. > > > --- > > man2/mmap.2 | 35 ++++++++++++++++++++++++++++++++++- > > 1 file changed, 34 insertions(+), 1 deletion(-) > > > > diff --git a/man2/mmap.2 b/man2/mmap.2 > > index 47c3148653be..b38ee6809327 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 > > +.BR MAP_SHARED_VALIDATE " (since Linux 4.15)" > > +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 > > @@ -134,7 +149,10 @@ It is unspecified whether changes made to the file after the > > .BR mmap () > > call are visible in the mapped region. > > .PP > > -Both of these flags are described in POSIX.1-2001 and POSIX.1-2008. > > +.B MAP_SHARED > > +and > > +.B MAP_PRIVATE > > +are described in POSIX.1-2001 and POSIX.1-2008. > > .PP > > In addition, zero or more of the following values can be ORed in > > .IR flags : > > @@ -352,6 +370,21 @@ 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. > > It feels like there's a word missing/unclear wording in the previous > line, before "using". Without that word, the sentence feels a bit > ambiguous. > > Should it be: > > persistent in a more efficient way *through the use of* appropriate > CPU instructions. > > or: > > persistent in a more efficient way *than using* appropriate CPU instructions. > > ? > > Is suspect the first is correct, but need to check. You're right, the first one is correct.
Hello Michael! On Thu 12-04-18 15:00:49, Michael Kerrisk (man-pages) wrote: > Hello Jan, > > I have applied your patch, and tweaked the text a little, and pushed > the result to the git repo. Thanks! > > +.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. > > It feels like there's a word missing/unclear wording in the previous > line, before "using". Without that word, the sentence feels a bit > ambiguous. > > Should it be: > > persistent in a more efficient way *through the use of* appropriate > CPU instructions. > > or: > > persistent in a more efficient way *than using* appropriate CPU instructions. > > ? > > Is suspect the first is correct, but need to check. Yes, the first is correct. Honza
Jan, Ross. On 12 April 2018 at 16:22, Jan Kara <jack@suse.cz> wrote: > Hello Michael! > > On Thu 12-04-18 15:00:49, Michael Kerrisk (man-pages) wrote: >> Hello Jan, >> >> I have applied your patch, and tweaked the text a little, and pushed >> the result to the git repo. > > Thanks! > >> > +.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. >> >> It feels like there's a word missing/unclear wording in the previous >> line, before "using". Without that word, the sentence feels a bit >> ambiguous. >> >> Should it be: >> >> persistent in a more efficient way *through the use of* appropriate >> CPU instructions. >> >> or: >> >> persistent in a more efficient way *than using* appropriate CPU instructions. >> >> ? >> >> Is suspect the first is correct, but need to check. > > Yes, the first is correct. Thanks for both checking that phrasing. In the end I decided to reword the sentence a bot more substantially: In conjunction with the use of appropriate CPU instructions, this provides users of such mappings with a more efficient way of making data modifica‐ tions persistent. Thanks, Michael
On Thu 12-04-18 20:20:12, Michael Kerrisk (man-pages) wrote: > > Thanks for both checking that phrasing. In the end I decided to reword > the sentence a bot more substantially: > > In conjunction with the use of appropriate CPU > instructions, this provides users of such mappings > with a more efficient way of making data modifica‐ > tions persistent. Great, thanks for the improvement! Honza
diff --git a/man2/mmap.2 b/man2/mmap.2 index 47c3148653be..b38ee6809327 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 +.BR MAP_SHARED_VALIDATE " (since Linux 4.15)" +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 @@ -134,7 +149,10 @@ It is unspecified whether changes made to the file after the .BR mmap () call are visible in the mapped region. .PP -Both of these flags are described in POSIX.1-2001 and POSIX.1-2008. +.B MAP_SHARED +and +.B MAP_PRIVATE +are described in POSIX.1-2001 and POSIX.1-2008. .PP In addition, zero or more of the following values can be ORed in .IR flags : @@ -352,6 +370,21 @@ 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