Re: [PATCH v2] mountlist: additional dummy FS names for Linux

[Pádraig Brady]

On 12/14/2012 04:17 AM, Jim Meyering wrote:
> Eric Wong wrote:
>
> > Jim Meyering <address@hidden> wrote:
> > > Eric Wong wrote:
> > > > * lib/mountlist.c (ME_DUMMY_0):
> > > >    additional dummy FS names for Linux systems.
> > > >    - "devpts" PTY slave filesystem
> > > >    - "fusectl" control filesystem for FUSE
> > > >    - "mqueue" enumerates POSIX message queues
> > > >    - "rpc_pipefs" kernel <-> userspace bridge for NFS
> > > >    - "sysfs" is for exporting kernel objects
> > > >    - "devfs" device filesystem for Linux 2.4 and FreeBSD
> > > >    There are likely more dummy FSes I am not aware of.
> > >
> > > Thanks.  I'll look at this Sat or Sunday.
> > > What's the motivation?  Have df hide those entries?
> >
> > It just seems right to mark those as dummy since they
> > aren't used for normal file storage.
> >
> > It allows cmogstored[1] to skip some entries and avoid extra
> > stat() and a tiny amount of memory allocation.  No big deal
> > with or without it.
> >
> > [1] http://bogomips.org/cmogstored/README
>
> Thanks.  I've tweaked the log and added a matching ChangeLog entry.
> Testing via df on my F18 laptop, diff -u <(src/df-prev) <(src/df)
> shows no difference.  What do people think of this entry from
> that F18 system?
>
>      devtmpfs         1538304        0   1538304   0% /dev
>
> If we're omitting "devfs", then should "devtmpfs" also be omitted?

I don't think "devtmpfs" should be marked as dummy
as there is storage associated with it.
I.E. you can write normal files to /dev and space will be consumed.

Note df already excludes most dummy file systems
by default by checking the size like:

  if (fsu.fsu_blocks == 0 && !show_all_fs && !show_listed_fs)
    return;

thanks,
Pádraig.