Re: [Qemu-devel] [PATCH v6 2/4] 9p: Added virtfs option 'multidevs=remap|forbid|warn'

[Greg Kurz <groug@kaod.org>]

On Sun, 01 Sep 2019 20:56:16 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> On Freitag, 30. August 2019 14:22:38 CEST Greg Kurz wrote:
> > Some more comments below.
> [snip]
> > > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > > index 8cc65c2c67..c96ea51116 100644
> > > --- a/hw/9pfs/9p.c
> > > +++ b/hw/9pfs/9p.c
> > > @@ -25,6 +25,7 @@
> > > 
> > >  #include "trace.h"
> > >  #include "migration/blocker.h"
> > >  #include "sysemu/qtest.h"
> [snip]
> > > @@ -3672,8 +3807,13 @@ int v9fs_device_realize_common(V9fsState *s, const
> > > V9fsTransport *t,> 
> > >          goto out;
> > >      
> > >      }
> > > 
> > > +    s->root_ino = stat.st_ino;
> > 
> > This isn't used anywhere. It looks like a leftover of the readdir fix
> > in v5.
> 
> Yes, both correct. I intentionally left it though, since I found it a natural 
> complement always capturing the root inode along to the root device.
> 

Fair enough. The local backend opens an fd to the root directory, to be used by
any access to the 9p share. I think root_dev/root_ino should be obtained with fstat()
on this fd, to be sure they are consistent. Maybe add an extra struct stat * argument
to the init function ? I'd rather see this done as a preparatory "backend to cache
9p root device/inode during init" patch.

> > >      s->dev_id = stat.st_dev;
> > > 
> > > +    /* QID path hash table. 1 entry ought to be enough for anybody ;) */
> > > +    qht_init(&s->qpp_table, qpp_lookup_func, 1, QHT_MODE_AUTO_RESIZE);
> > > +    s->qp_prefix_next = 1; /* reserve 0 to detect overflow */
> > > +
> > > 
> > >      s->ctx.fst = &fse->fst;
> > >      fsdev_throttle_init(s->ctx.fst);
> > > 
> > > @@ -3687,6 +3827,7 @@ out:
> > >          }
> > >          g_free(s->tag);
> > >          g_free(s->ctx.fs_root);
> > > 
> > > +        qpp_table_destroy(&s->qpp_table);
> > > 
> > >          v9fs_path_free(&path);
> > >      
> > >      }
> > >      return rc;
> > > 
> > > @@ -3699,6 +3840,7 @@ void v9fs_device_unrealize_common(V9fsState *s,
> > > Error **errp)> 
> > >      }
> > >      fsdev_throttle_cleanup(s->ctx.fst);
> > >      g_free(s->tag);
> > > 
> > > +    qpp_table_destroy(&s->qpp_table);
> > > 
> > >      g_free(s->ctx.fs_root);
> > >  
> > >  }
> > > 
> > > diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
> > > index 5e316178d5..a283b0193e 100644
> > > --- a/hw/9pfs/9p.h
> > > +++ b/hw/9pfs/9p.h
> > > @@ -8,6 +8,7 @@
> > > 
> > >  #include "fsdev/9p-iov-marshal.h"
> > >  #include "qemu/thread.h"
> > >  #include "qemu/coroutine.h"
> > > 
> > > +#include "qemu/qht.h"
> > > 
> > >  enum {
> > >  
> > >      P9_TLERROR = 6,
> > > 
> > > @@ -235,6 +236,15 @@ struct V9fsFidState
> > > 
> > >      V9fsFidState *rclm_lst;
> > >  
> > >  };
> > > 
> > > +#define QPATH_INO_MASK        ((1ULL << 48) - 1)
> > > +
> > > +/* QID path prefix entry, see stat_to_qid */
> > > +typedef struct {
> > > +    dev_t dev;
> > > +    uint16_t ino_prefix;
> > > +    uint16_t qp_prefix;
> > > +} QppEntry;
> > > +
> > > 
> > >  struct V9fsState
> > >  {
> > >  
> > >      QLIST_HEAD(, V9fsPDU) free_list;
> > > 
> > > @@ -256,7 +266,10 @@ struct V9fsState
> > > 
> > >      Error *migration_blocker;
> > >      V9fsConf fsconf;
> > >      V9fsQID root_qid;
> > > 
> > > +    ino_t root_ino;
> > 
> > Thinking again, I'm wondering if root_ino and dev_id could be used
> > instead of root_qid in v9fs_walk()... Would you have a look at that
> > if you decide to fix the readdir issue ?
> 
> I keep it in mind when looking at the postponed readdir() issue again.
> 
> > >      dev_t dev_id;
> > > 
> > > +    struct qht qpp_table;
> > > +    uint16_t qp_prefix_next;
> > > 
> > >  };
> > >  
> > >  /* 9p2000.L open flags */
> > > 
>