ceph: use __getname/__putname in ceph_mdsc_build_path

Al suggested we get rid of the kmalloc here and just use __getname
and __putname to get a full PATH_MAX pathname buffer.

Since we build the path in reverse, we continue to return a pointer
to the beginning of the string and the length, and add a new helper
to free the thing at the end.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

3 files changed, 36 insertions, 39 deletions

diff --git a/fs/ceph/debugfs.c b/fs/ceph/debugfs.c
index 777f6ceb5259..b014fc7d4e3c 100644
--- a/fs/ceph/debugfs.c
+++ b/fs/ceph/debugfs.c
@@ -88,7 +88,7 @@ static int mdsc_show(struct seq_file *s, void *p)
                                    req->r_dentry,
                                    path ? path : "");
                         spin_unlock(&req->r_dentry->d_lock);
-                        kfree(path);
+                        ceph_mdsc_free_path(path, pathlen);
                 } else if (req->r_path1) {
                         seq_printf(s, " #%llx/%s", req->r_ino1.ino,
                                    req->r_path1);
@@ -108,7 +108,7 @@ static int mdsc_show(struct seq_file *s, void *p)
                                    req->r_old_dentry,
                                    path ? path : "");
                         spin_unlock(&req->r_old_dentry->d_lock);
-                        kfree(path);
+                        ceph_mdsc_free_path(path, pathlen);
                 } else if (req->r_path2 && req->r_op != CEPH_MDS_OP_SYMLINK) {
                         if (req->r_ino2.ino)
                                 seq_printf(s, " #%llx/%s", req->r_ino2.ino,
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 7af722834348..d29f6c094f7c 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2094,39 +2094,24 @@ char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *pbase,
 {
         struct dentry *temp;
         char *path;
-        int len, pos;
+        int pos;
         unsigned seq;
         u64 base;
 
         if (!dentry)
                 return ERR_PTR(-EINVAL);
 
-retry:
-        len = 0;
-        seq = read_seqbegin(&rename_lock);
-        rcu_read_lock();
-        for (temp = dentry; !IS_ROOT(temp);) {
-                struct inode *inode = d_inode(temp);
-                if (inode && ceph_snap(inode) == CEPH_SNAPDIR)
-                        len++;  /* slash only */
-                else if (stop_on_nosnap && inode &&
-                         ceph_snap(inode) == CEPH_NOSNAP)
-                        break;
-                else
-                        len += 1 + temp->d_name.len;
-                temp = temp->d_parent;
-        }
-        rcu_read_unlock();
-        if (len)
-                len--;  /* no leading '/' */
-
-        path = kmalloc(len+1, GFP_NOFS);
+        path = __getname();
         if (!path)
                 return ERR_PTR(-ENOMEM);
-        pos = len;
-        path[pos] = 0;  /* trailing null */
+retry:
+        pos = PATH_MAX - 1;
+        path[pos] = '\0';
+
+        seq = read_seqbegin(&rename_lock);
         rcu_read_lock();
-        for (temp = dentry; !IS_ROOT(temp) && pos != 0; ) {
+        temp = dentry;
+        for (;;) {
                 struct inode *inode;
 
                 spin_lock(&temp->d_lock);
@@ -2144,32 +2129,38 @@ retry:
                                 spin_unlock(&temp->d_lock);
                                 break;
                         }
-                        strncpy(path + pos, temp->d_name.name,
-                                temp->d_name.len);
+                        memcpy(path + pos, temp->d_name.name, temp->d_name.len);
                 }
                 spin_unlock(&temp->d_lock);
-                if (pos)
-                        path[--pos] = '/';
                 temp = temp->d_parent;
+
+                /* Are we at the root? */
+                if (IS_ROOT(temp))
+                        break;
+
+                /* Are we out of buffer? */
+                if (--pos < 0)
+                        break;
+
+                path[pos] = '/';
         }
         base = ceph_ino(d_inode(temp));
         rcu_read_unlock();
-        if (pos != 0 || read_seqretry(&rename_lock, seq)) {
+        if (pos < 0 || read_seqretry(&rename_lock, seq)) {
                 pr_err("build_path did not end path lookup where "
-                       "expected, namelen is %d, pos is %d\n", len, pos);
+                       "expected, pos is %d\n", pos);
                 /* presumably this is only possible if racing with a
                    rename of one of the parent directories (we can not
                    lock the dentries above us to prevent this, but
                    retrying should be harmless) */
-                kfree(path);
                 goto retry;
         }
 
         *pbase = base;
-        *plen = len;
+        *plen = PATH_MAX - 1 - pos;
         dout("build_path on %p %d built %llx '%.*s'\n",
-             dentry, d_count(dentry), base, len, path);
-        return path;
+             dentry, d_count(dentry), base, *plen, path + pos);
+        return path + pos;
 }
 
 static int build_dentry_path(struct dentry *dentry, struct inode *dir,
@@ -2376,10 +2367,10 @@ static struct ceph_msg *create_request_message(struct ceph_mds_client *mdsc,
 
 out_free2:
         if (freepath2)
-                kfree((char *)path2);
+                ceph_mdsc_free_path((char *)path2, pathlen2);
 out_free1:
         if (freepath1)
-                kfree((char *)path1);
+                ceph_mdsc_free_path((char *)path1, pathlen1);
 out:
         return msg;
 }
@@ -3451,7 +3442,7 @@ out_freeflocks:
                 ceph_pagelist_encode_string(pagelist, path, pathlen);
                 ceph_pagelist_append(pagelist, &rec, sizeof(rec.v1));
 out_freepath:
-                kfree(path);
+                ceph_mdsc_free_path(path, pathlen);
         }
 
 out_err:
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 0d1f673a5689..ebcad5afc87b 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -492,6 +492,12 @@ extern int ceph_iterate_session_caps(struct ceph_mds_session *session,
                                      void *arg);
 extern void ceph_mdsc_pre_umount(struct ceph_mds_client *mdsc);
 
+static inline void ceph_mdsc_free_path(char *path, int len)
+{
+        if (path)
+                __putname(path - (PATH_MAX - 1 - len));
+}
+
 extern char *ceph_mdsc_build_path(struct dentry *dentry, int *plen, u64 *base,
                                   int stop_on_nosnap);