9p: Replace the fidlist with an IDR

The p9_idpool being used to allocate the IDs uses an IDR to allocate
the IDs ... which we then keep in a doubly-linked list, rather than in
the IDR which allocated them.  We can use an IDR directly which saves
two pointers per p9_fid, and a tiny memory allocation per p9_client.

Link: http://lkml.kernel.org/r/20180711210225.19730-4-willy@infradead.org
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>

include/net/9p/client.h

@@ -27,6 +27,7 @@
 #define NET_9P_CLIENT_H
 
 #include <linux/utsname.h>
+#include <linux/idr.h>
 
 /* Number of requests per row */
 #define P9_ROW_MAXTAG 255
@@ -128,8 +129,7 @@ struct p9_req_t {
  * @proto_version: 9P protocol version to use
  * @trans_mod: module API instantiated with this client
  * @trans: tranport instance state and API
- * @fidpool: fid handle accounting for session
+ * @fids: All active FID handles
- * @fidlist: List of active fid handles
  * @tagpool - transaction id accounting for session
  * @reqs - 2D array of requests
  * @max_tag - current maximum tag id allocated
@@ -169,8 +169,7 @@ struct p9_client {
 		} tcp;
 	} trans_opts;
 
-	struct p9_idpool *fidpool;
+	struct idr fids;
-	struct list_head fidlist;
 
 	struct p9_idpool *tagpool;
 	struct p9_req_t *reqs[P9_ROW_MAXTAG];
@@ -188,7 +187,6 @@ struct p9_client {
  * @iounit: the server reported maximum transaction size for this file
  * @uid: the numeric uid of the local user who owns this handle
  * @rdir: readdir accounting structure (allocated on demand)
- * @flist: per-client-instance fid tracking
  * @dlist: per-dentry fid tracking
  *
  * TODO: This needs lots of explanation.
@@ -204,7 +202,6 @@ struct p9_fid {
 
 	void *rdir;
 
-	struct list_head flist;
 	struct hlist_node dlist;	/* list of all fids attached to a dentry */
 };
 

net/9p/client.c

@@ -909,30 +909,29 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt)
 {
 	int ret;
 	struct p9_fid *fid;
-	unsigned long flags;
 
 	p9_debug(P9_DEBUG_FID, "clnt %p\n", clnt);
 	fid = kmalloc(sizeof(struct p9_fid), GFP_KERNEL);
 	if (!fid)
 		return NULL;
 
-	ret = p9_idpool_get(clnt->fidpool);
-	if (ret < 0)
-		goto error;
-	fid->fid = ret;
-
 	memset(&fid->qid, 0, sizeof(struct p9_qid));
 	fid->mode = -1;
 	fid->uid = current_fsuid();
 	fid->clnt = clnt;
 	fid->rdir = NULL;
-	spin_lock_irqsave(&clnt->lock, flags);
+	fid->fid = 0;
-	list_add(&fid->flist, &clnt->fidlist);
-	spin_unlock_irqrestore(&clnt->lock, flags);
 
-	return fid;
+	idr_preload(GFP_KERNEL);
+	spin_lock_irq(&clnt->lock);
+	ret = idr_alloc_u32(&clnt->fids, fid, &fid->fid, P9_NOFID - 1,
+			    GFP_NOWAIT);
+	spin_unlock_irq(&clnt->lock);
+	idr_preload_end();
+
+	if (!ret)
+		return fid;
 
-error:
 	kfree(fid);
 	return NULL;
 }
@@ -944,9 +943,8 @@ static void p9_fid_destroy(struct p9_fid *fid)
 
 	p9_debug(P9_DEBUG_FID, "fid %d\n", fid->fid);
 	clnt = fid->clnt;
-	p9_idpool_put(fid->fid, clnt->fidpool);
 	spin_lock_irqsave(&clnt->lock, flags);
-	list_del(&fid->flist);
+	idr_remove(&clnt->fids, fid->fid);
 	spin_unlock_irqrestore(&clnt->lock, flags);
 	kfree(fid->rdir);
 	kfree(fid);
@@ -1029,7 +1027,7 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
 	memcpy(clnt->name, client_id, strlen(client_id) + 1);
 
 	spin_lock_init(&clnt->lock);
-	INIT_LIST_HEAD(&clnt->fidlist);
+	idr_init(&clnt->fids);
 
 	err = p9_tag_init(clnt);
 	if (err < 0)
@@ -1049,18 +1047,12 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
 		goto destroy_tagpool;
 	}
 
-	clnt->fidpool = p9_idpool_create();
-	if (IS_ERR(clnt->fidpool)) {
-		err = PTR_ERR(clnt->fidpool);
-		goto put_trans;
-	}
-
 	p9_debug(P9_DEBUG_MUX, "clnt %p trans %p msize %d protocol %d\n",
 		 clnt, clnt->trans_mod, clnt->msize, clnt->proto_version);
 
 	err = clnt->trans_mod->create(clnt, dev_name, options);
 	if (err)
-		goto destroy_fidpool;
+		goto put_trans;
 
 	if (clnt->msize > clnt->trans_mod->maxsize)
 		clnt->msize = clnt->trans_mod->maxsize;
@@ -1073,8 +1065,6 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
 
 close_trans:
 	clnt->trans_mod->close(clnt);
-destroy_fidpool:
-	p9_idpool_destroy(clnt->fidpool);
 put_trans:
 	v9fs_put_trans(clnt->trans_mod);
 destroy_tagpool:
@@ -1087,7 +1077,8 @@ EXPORT_SYMBOL(p9_client_create);
 
 void p9_client_destroy(struct p9_client *clnt)
 {
-	struct p9_fid *fid, *fidptr;
+	struct p9_fid *fid;
+	int id;
 
 	p9_debug(P9_DEBUG_MUX, "clnt %p\n", clnt);
 
@@ -1096,14 +1087,11 @@ void p9_client_destroy(struct p9_client *clnt)
 
 	v9fs_put_trans(clnt->trans_mod);
 
-	list_for_each_entry_safe(fid, fidptr, &clnt->fidlist, flist) {
+	idr_for_each_entry(&clnt->fids, fid, id) {
 		pr_info("Found fid %d not clunked\n", fid->fid);
 		p9_fid_destroy(fid);
 	}
 
-	if (clnt->fidpool)
-		p9_idpool_destroy(clnt->fidpool);
-
 	p9_tag_cleanup(clnt);
 
 	kfree(clnt);