Re: [Qemu-devel] [PATCH 3/5] virtiofsd: rename inode->refcount to inode->nlookup

[Dr. David Alan Gilbert]

* Stefan Hajnoczi (address@hidden) wrote:
> This reference counter plays a specific role in the FUSE protocol.  It's
> not a generic object reference counter and the FUSE kernel code calls it
> "nlookup".
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>


Reviewed-by: Dr. David Alan Gilbert <address@hidden>

> ---
>  contrib/virtiofsd/passthrough_ll.c | 36 ++++++++++++++++++++----------
>  1 file changed, 24 insertions(+), 12 deletions(-)
> 
> diff --git a/contrib/virtiofsd/passthrough_ll.c 
> b/contrib/virtiofsd/passthrough_ll.c
> index e1d729d26b..135123366a 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -97,7 +97,19 @@ struct lo_inode {
>       int fd;
>       bool is_symlink;
>       struct lo_key key;
> -     uint64_t refcount; /* protected by lo->mutex */
> +
> +     /* This counter keeps the inode alive during the FUSE session.
> +      * Incremented when the FUSE inode number is sent in a reply
> +      * (FUSE_LOOKUP, FUSE_READDIRPLUS, etc).  Decremented when an inode is
> +      * released by requests like FUSE_FORGET, FUSE_RMDIR, FUSE_RENAME, etc.
> +      *
> +      * Note that this value is untrusted because the client can manipulate
> +      * it arbitrarily using FUSE_FORGET requests.
> +      *
> +      * Protected by lo->mutex.
> +      */
> +     uint64_t nlookup;
> +
>       uint64_t version_offset;
>       uint64_t ireg_refid;
>       fuse_ino_t fuse_ino;
> @@ -485,7 +497,7 @@ retry:
>       if (last == path) {
>               p = &lo->root;
>               pthread_mutex_lock(&lo->mutex);
> -             p->refcount++;
> +             p->nlookup++;
>               pthread_mutex_unlock(&lo->mutex);
>       } else {
>               *last = '\0';
> @@ -688,8 +700,8 @@ static struct lo_inode *lo_find(struct lo_data *lo, 
> struct stat *st)
>       pthread_mutex_lock(&lo->mutex);
>       p = g_hash_table_lookup(lo->inodes, &key);
>       if (p) {
> -             assert(p->refcount > 0);
> -             p->refcount++;
> +             assert(p->nlookup > 0);
> +             p->nlookup++;
>       }
>       pthread_mutex_unlock(&lo->mutex);
>  
> @@ -797,7 +809,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t 
> parent, const char *name,
>                       goto out_err;
>  
>               inode->is_symlink = S_ISLNK(e->attr.st_mode);
> -             inode->refcount = 1;
> +             inode->nlookup = 1;
>               inode->fd = newfd;
>               newfd = -1;
>               inode->key.ino = e->attr.st_ino;
> @@ -1051,7 +1063,7 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, 
> fuse_ino_t parent,
>               goto out_err;
>  
>       pthread_mutex_lock(&lo->mutex);
> -     inode->refcount++;
> +     inode->nlookup++;
>       pthread_mutex_unlock(&lo->mutex);
>       e.ino = inode->fuse_ino;
>       update_version(lo, inode);
> @@ -1200,9 +1212,9 @@ static void unref_inode(struct lo_data *lo, struct 
> lo_inode *inode, uint64_t n)
>               return;
>  
>       pthread_mutex_lock(&lo->mutex);
> -     assert(inode->refcount >= n);
> -     inode->refcount -= n;
> -     if (!inode->refcount) {
> +     assert(inode->nlookup >= n);
> +     inode->nlookup -= n;
> +     if (!inode->nlookup) {
>               lo_map_remove(&lo->ino_map, inode->fuse_ino);
>                  g_hash_table_remove(lo->inodes, &inode->key);
>               if (g_hash_table_size(inode->posix_locks)) {
> @@ -1225,7 +1237,7 @@ static int unref_all_inodes_cb(gpointer key, gpointer 
> value,
>       struct lo_inode *inode  = value;
>       struct lo_data *lo = user_data;
>  
> -     inode->refcount = 0;
> +     inode->nlookup = 0;
>       lo_map_remove(&lo->ino_map, inode->fuse_ino);
>       close(inode->fd);
>  
> @@ -1252,7 +1264,7 @@ static void lo_forget_one(fuse_req_t req, fuse_ino_t 
> ino, uint64_t nlookup)
>       if (lo_debug(req)) {
>               fuse_debug("  forget %lli %lli -%lli\n",
>                          (unsigned long long) ino,
> -                        (unsigned long long) inode->refcount,
> +                        (unsigned long long) inode->nlookup,
>                          (unsigned long long) nlookup);
>       }
>  
> @@ -2581,7 +2593,7 @@ static void setup_root(struct lo_data *lo, struct 
> lo_inode *root)
>       root->fd = fd;
>       root->key.ino = stat.st_ino;
>       root->key.dev = stat.st_dev;
> -     root->refcount = 2;
> +     root->nlookup = 2;
>  }
>  
>  static void setup_proc_self_fd(struct lo_data *lo)
> -- 
> 2.21.0
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK