On Fri, Apr 01, 2011 at 12:12:34PM +0200, Miklos Szeredi wrote:
> On Fri, 1 Apr 2011, Karel Zak wrote:
> > On Fri, Apr 01, 2011 at 10:45:48AM +0200, Miklos Szeredi wrote:
> > > On Fri, 01 Apr 2011, Aneesh Kumar K. V wrote:
> > > > On Thu, 31 Mar 2011 22:24:01 +0200, victor.vde@xxxxxxxxx wrote:
> > > > > /proc/self/mountinfo on Linux v2.6.39-rc1 includes the UUID of ext4
> > > > > and ext3 mounts, for example:
> > > > >
> > > > > 15 1 8:3 / / rw,noatime uuid:c645234d-9756-4d84-825e-6fe999252a34 - ext4 /dev/sda3 rw,user_xattr,acl,barrier=1,data=ordered
> > > > >
> > > > > It seems the hyphens in the uuid confuse the parser
> > > > > mnt_parse_mountinfo_line in tab_parse.c of libmount in util-linux.
> > > >
> > > > shouldn't the parser look for " " followed by "-" followed by " " as the
> > > > field seperator ?
> > > >
> > > > I am adding Miklos and Ram Pai to CC to check whether the kernel or the libmount
> > > > should be fixed ?
> > >
> > > I think libmount should be fixed, though there is always the question
> > > of backward compatibility.
> >
> > The parser uses
> >
> > rc = sscanf(s, "%u " /* (1) id */
> > "%u " /* (2) parent */
> > "%u:%u " /* (3) maj:min */
> > "%ms " /* (4) mountroot */
> > "%ms " /* (5) target */
> > "%ms" /* (6) vfs options (fs-independent) */
> > "%*[^-]" /* (7) optional fields */
>
> So this says, "skip everything up to the first hyphen", even though
> the rule might be better expressed as "skip all space delimited words
> up to the first standalone hyphen". I guess that's not possible to
> express with a scanf expression, though.
Yes, I'll probably use two sscanf(), %n and strstr(), something like:
rc = sscanf(s, "%u " /* (1) id */
"%u " /* (2) parent */
"%u:%u " /* (3) maj:min */
"%ms " /* (4) mountroot */
"%ms " /* (5) target */
"%ms" /* (6) vfs options (fs-independent) */
"%n",
&id,
&parent,
&maj, &min,
&root,
&target,
&vfs_optstr,
&end);
s += end;
/* (7) optional fields, terminated by " - " */
p = strstr(s, " - ");
if (p)
s = p + 3;
rc += sscanf(s, "%ms " /* (8) FS type */
"%ms " /* (9) source */
"%ms", /* (10) fs options (fs specific) */
&fstype,
&src,
&fs_optstr);
...or anyone has a better idea?
> > It calls unmangle_string() for all fields, so all sequences should be
> > decoded.
>
> Okay, so the kernel can simply escape the troublesome hyphens, which
> would make the human parsing of /proc/pid/mountinfo more difficult but
> at least would fix compatibility with util-linux's parser.
Hmm.. IMHO it will be better to fix the parsers in libmount and systemd. The
both projects are young, nobody will be surprised with bugs :-)
I think the example in Documentation/filesystems/proc.txt is pretty
obvious, the separator is an extra field with " - ".
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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