nilfs2: get rid of sget use for acquiring nilfs object

This will change the way to obtain nilfs object in nilfs_get_sb()
function.

Previously, a preliminary sget() call was performed, and the nilfs
object was acquired from a super block instance found by the sget()
call.

This patch, instead, instroduces a new dedicated function
find_or_create_nilfs(); as the name implies, the function finds an
existent nilfs object from a global list or creates a new one if no
object is found on the device.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 54 insertions, 3 deletions

diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index a91f15b8673c..45dbf6a61744 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -35,6 +35,10 @@
 #include "seglist.h"
 #include "segbuf.h"
 
+
+static LIST_HEAD(nilfs_objects);
+static DEFINE_SPINLOCK(nilfs_lock);
+
 void nilfs_set_last_segment(struct the_nilfs *nilfs,
                             sector_t start_blocknr, u64 seq, __u64 cno)
 {
@@ -55,7 +59,7 @@ void nilfs_set_last_segment(struct the_nilfs *nilfs,
  * Return Value: On success, pointer to the_nilfs is returned.
  * On error, NULL is returned.
  */
-struct the_nilfs *alloc_nilfs(struct block_device *bdev)
+static struct the_nilfs *alloc_nilfs(struct block_device *bdev)
 {
         struct the_nilfs *nilfs;
 
@@ -69,6 +73,7 @@ struct the_nilfs *alloc_nilfs(struct block_device *bdev)
         atomic_set(&nilfs->ns_ndirtyblks, 0);
         init_rwsem(&nilfs->ns_sem);
         mutex_init(&nilfs->ns_writer_mutex);
+        INIT_LIST_HEAD(&nilfs->ns_list);
         INIT_LIST_HEAD(&nilfs->ns_supers);
         spin_lock_init(&nilfs->ns_last_segment_lock);
         nilfs->ns_gc_inodes_h = NULL;
@@ -78,6 +83,45 @@ struct the_nilfs *alloc_nilfs(struct block_device *bdev)
 }
 
 /**
+ * find_or_create_nilfs - find or create nilfs object
+ * @bdev: block device to which the_nilfs is related
+ *
+ * find_nilfs() looks up an existent nilfs object created on the
+ * device and gets the reference count of the object.  If no nilfs object
+ * is found on the device, a new nilfs object is allocated.
+ *
+ * Return Value: On success, pointer to the nilfs object is returned.
+ * On error, NULL is returned.
+ */
+struct the_nilfs *find_or_create_nilfs(struct block_device *bdev)
+{
+        struct the_nilfs *nilfs, *new = NULL;
+
+ retry:
+        spin_lock(&nilfs_lock);
+        list_for_each_entry(nilfs, &nilfs_objects, ns_list) {
+                if (nilfs->ns_bdev == bdev) {
+                        get_nilfs(nilfs);
+                        spin_unlock(&nilfs_lock);
+                        if (new)
+                                put_nilfs(new);
+                        return nilfs; /* existing object */
+                }
+        }
+        if (new) {
+                list_add_tail(&new->ns_list, &nilfs_objects);
+                spin_unlock(&nilfs_lock);
+                return new; /* new object */
+        }
+        spin_unlock(&nilfs_lock);
+
+        new = alloc_nilfs(bdev);
+        if (new)
+                goto retry;
+        return NULL; /* insufficient memory */
+}
+
+/**
  * put_nilfs - release a reference to the_nilfs
  * @nilfs: the_nilfs structure to be released
  *
@@ -86,13 +130,20 @@ struct the_nilfs *alloc_nilfs(struct block_device *bdev)
  */
 void put_nilfs(struct the_nilfs *nilfs)
 {
-        if (!atomic_dec_and_test(&nilfs->ns_count))
+        spin_lock(&nilfs_lock);
+        if (!atomic_dec_and_test(&nilfs->ns_count)) {
+                spin_unlock(&nilfs_lock);
                 return;
+        }
+        list_del_init(&nilfs->ns_list);
+        spin_unlock(&nilfs_lock);
+
         /*
-         * Increment of ns_count never occur below because the caller
+         * Increment of ns_count never occurs below because the caller
          * of get_nilfs() holds at least one reference to the_nilfs.
          * Thus its exclusion control is not required here.
          */
+
         might_sleep();
         if (nilfs_loaded(nilfs)) {
                 nilfs_mdt_clear(nilfs->ns_sufile);