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.

Signed-off-by: Matthew Wilcox <wi...@infradead.org>
---
 include/net/9p/client.h |  9 +++------
 net/9p/client.c         | 44 +++++++++++++++--------------------------
 2 files changed, 19 insertions(+), 34 deletions(-)

diff --git a/include/net/9p/client.h b/include/net/9p/client.h
index 7af9d769b97d..e405729cd1c7 100644
--- a/include/net/9p/client.h
+++ b/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
- * @fidlist: List of active fid handles
+ * @fids: All 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 list_head fidlist;
+       struct idr fids;
 
        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 */
 };
 
diff --git a/net/9p/client.c b/net/9p/client.c
index 389a2904b7b3..b89c7298267c 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -908,30 +908,29 @@ 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);
-       list_add(&fid->flist, &clnt->fidlist);
-       spin_unlock_irqrestore(&clnt->lock, flags);
+       fid->fid = 0;
 
-       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;
 }
@@ -943,9 +942,8 @@ 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);
@@ -1028,7 +1026,7 @@ 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)
@@ -1048,18 +1046,12 @@ 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;
@@ -1072,8 +1064,6 @@ 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:
@@ -1086,7 +1076,8 @@ 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);
 
@@ -1095,14 +1086,11 @@ 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);
-- 
2.18.0

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