Re: [uml-devel] UML hostfs bugs

["wang lianwei" <lianwei.wang@gmail.com>]

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Answers:

1. I test it on ext3 filesystem.

2. You are right. Sometimes the pos telldir returned is not the next entry
offset. just as your point out:
      position 0 -> readdir "." -> you call telldir -> it _again_ says
you're at 0.

3. I also try to resolve it by remove the seekdir(only use the
sequence readdir call), It is also worked.

--- linux-2.6.x/fs/hostfs/hostfs_kern.c 2006-04-12 15:12:51.000000000 +0800
+++ linux-2.6.10-src/fs/hostfs/hostfs_kern.c      2006-08-14 18:25:
13.772237744 +0800
@@ -338,6 +338,7 @@
        kfree(name);
        if(dir == NULL) return(-error);
        next = file->f_pos;
+       seekdir(dir,next);
        while((name = read_dir(dir, &next, &ino, &len)) != NULL){
                error = (*filldir)(ent, name, len, file->f_pos,
                                   ino, DT_UNKNOWN);


--- linux-2.6.x/fs/hostfs/hostfs_user.c 2006-04-12 15:12:52.000000000 +0800
+++ linux-2.6.10-src/fs/hostfs/hostfs_user.c      2006-08-14 18:36:
24.276305632 +0800
@@ -122,7 +122,6 @@
        DIR *dir = stream;
        struct dirent *ent;

-       seekdir(dir, *pos);
        ent = readdir(dir);
        if(ent == NULL) return(NULL);
        *len_out = strlen(ent->d_name);




2006/8/13, Blaisorblade <blaisorblade@yahoo.it>:
>
> On Thursday 10 August 2006 17:42, wang lianwei wrote:
> > Hi all,
> >
> > There is a bug with UML kernel, some host directory can not be read, for
>
> > example "ls /mnt/host/usr/lib", this command is dead until you press
> > CTRL+c. I test it with Redhat Enterprise Linux 4.
>
> Yes, this has been reported various times but difficult to reproduce, so
> we're
> very happy somebody diagnosed it, and I'd be interested in understanding
> it
> better.
>
> On which filesystem (ext3, reiserfs, what else) lays /usr/lib on the host?
>
> This is because the UML read host directory through opendir, seekdir,
> > readdir and telldir. When get the dir stream offset through telldir, it
> > always return 0 on some directory, for example".",
>
> Can you elaborate on this? (And if possible post some details, like a
> strace)
>
> What I've understood is:
>
> position 0 -> you read "." -> you call telldir -> it _again_ says you're
> at 0?
>
> I can maybe understand why it could happen. I'd be more interested in
> checking
> if a simple sequence of readdir() calls (without seekdir()) would work
> (probably write a standalone test program, it will be easier to use and
> debug) and why read_dir needs to do seekdir (I think it's done to handle
> calls to seekdir by the underlying process, but there should be different
> ways to do it).
>
> > I don't know why? But
> > we can fix it as follows although the next dir entry offset is not
> exact:
>
> > Modify the fs/hostfs/hostfs_user.c file, update the read_dir function,
> >
> > char *read_dir(void *stream, unsigned long long *pos,
> >                unsigned long long *ino_out, int *len_out)
> > {
> >         DIR *dir = stream;
> >         struct dirent *ent;
> >         unsigned long long oldpos;
> >
> >         oldpos = *pos;
> >
> >         seekdir(dir, *pos);
> >         ent = readdir(dir);
> >         if(ent == NULL)
> >         {
> >                 return(NULL);
> >         }
> >         *len_out = strlen(ent->d_name);
> >         *ino_out = ent->d_ino;
> >         *pos = telldir(dir);
> >
> >         /* Fix the telldir return 0 error */
> >         if (*pos == 0)
> >                 *pos = oldpos + *len_out;
> >
> >         return(ent->d_name);
> > }
> >
> > although the next offset is not exact, but the readdir can get the next
> > entry correct.
>
> This probably depends heavily on the underlying filesystem...
>
> > Can anyone give a better solution?
>
> I can't yet, but maybe with your help we'll be able.
> --
> Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
> Paolo Giarrusso, aka Blaisorblade
> http://www.user-mode-linux.org/~blaisorblade
> Chiacchiera con i tuoi amici in tempo reale!
> http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com
>
>

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