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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Stefan Hajnoczi (stefanha@redhat.com) 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 <stefanha@redhat.com>


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  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 / dgilbert@redhat.com / Manchester, UK