Re: [PATCH] statfs.2 does not describe f_flag field

[Jan Chaloupka <jchaloup-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On 02/04/2015 12:51 PM, Michael Kerrisk (man-pages) wrote:
> Hi Jan,
>
> On 4 February 2015 at 09:48, Jan Chaloupka <jchaloup-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>> Based on kernel commit [1], new flag f_flag is added to statfs struct.
>>
>> Before kernel 2.6.36, glibc's statvfs.f_flags was computed be iterating
>> through all mounted points. This was inefficient and could cause a delay.
>> Since kernel 2.6.36, statfs struct has new field f_flag, which already
>> extracts mount options without iterating through mount point.
>> statfs.f_flag flags of glibc and kernel are the same (plus kernel adds
>> additional flag ST_VALID used only internally). So no matter what version
>> of kernel is used, flags does not change.
>>
>> Flags used in statfs.f_flags can be enumerated from upstreams's
>> glibc/internal_statvfs.c, lines 155-173. Nine flags in sum:
>>
>> ST_RDONLY = 1
>> ST_NOSUID = 2
>> ST_NODEV = 4
>> ST_NOEXEC = 8
>> ST_SYNCHRONOUS = 16
>> ST_MANDLOCK = 64
>> ST_NOATIME = 1024
>> ST_NODIRATIME = 2048
>> ST_RELATIME = 4096
>>
>> This patch describes missing flag.
>>
>> [1] https://github.com/torvalds/linux/commit/365b18189789bfa1acd9939e6312b8a4b4577b28
> Thanks for the heads up. But this patch is a bit muddled, since it
> mixes details about statfs(2) and statvfs(3).

Yes. As kernel copied all the flags, it is now duplicated. But you are 
right it more suites for statvfs(2).

>   I've instead made some more detailed changes for the statfs(2) and statvfs(2) pages.
>

Thanks.

>
> Thanks,
>
> Michael
>
>
>> Signed-off-by: Jan Chaloupka <jchaloup-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> ---
>>   man2/statfs.2 |   28 +++++++++++++++++++++++++++-
>>   1 file changed, 27 insertions(+), 1 deletion(-)
>>
>> diff --git a/man2/statfs.2 b/man2/statfs.2
>> index 714bc7c..46cfa5f 100644
>> --- a/man2/statfs.2
>> +++ b/man2/statfs.2
>> @@ -65,7 +65,9 @@ struct statfs {
>>       fsid_t       f_fsid;    /* filesystem id */
>>       __SWORD_TYPE f_namelen; /* maximum length of filenames */
>>       __SWORD_TYPE f_frsize;  /* fragment size (since Linux 2.6) */
>> -    __SWORD_TYPE f_spare[5];
>> +    __SWORD_TYPE f_flags;   /* mount flags of filesystem
>> +                               (since Linux 2.6.36) */
>> +    __SWORD_TYPE f_spare[4];
>>   };
>>
>>   Filesystem types:
>> @@ -146,6 +148,30 @@ Most of these MAGIC constants are defined in
>>   .IR /usr/include/linux/magic.h ,
>>   and some are hardcoded in kernel sources.
>>   .PP
>> +Mount flags of
>> +.I f_flags
>> +field are extracted from an option string of a mount point defined in
>> +.BR mount (8).
>> +The field can be combination of the following flags
>> +(corresponding mount options are in the right column):
>> +.in
>> +.nf
>> +
>> +   ST_RDONLY          ro
>> +   ST_NOSUID          nosuid
>> +   ST_NOEXEC          noexec
>> +   ST_NODEV           nodev
>> +   ST_SYNCHRONOUS     sync
>> +   ST_MANDLOCK        mand
>> +   ST_NOATIME         noatime
>> +   ST_NODIRATIME      nodiratime
>> +   ST_RELATIME        relatime
>> +
>> +.fi
>> +.in
>> +For kernel less than 2.6.36 option flags are extracted by iterating
>> +through individual mount points which can be inefficient and cause delay.
>> +.PP
>>   Nobody knows what
>>   .I f_fsid
>>   is supposed to contain (but see below).
>>
>
>
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