Inode: Allow external initialisers

To allow XFS to combine the XFS and linux inodes into a single
structure, we need to drive inode lookup from the XFS inode cache,
not the generic inode cache. This means that we need initialise a
struct inode from a context outside alloc_inode() as it is no longer
used by XFS.

Factor and export the struct inode initialisation code from
alloc_inode() to inode_init_always() as a counterpart to
inode_init_once().  i.e. we have to call this init function for each
inode instantiation (always), as opposed inode_init_once() which is
only called on slab object instantiation (once).

Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

2 files changed, 79 insertions, 62 deletions

diff --git a/fs/inode.c b/fs/inode.c
index 0487ddba1397..e7ee99907d60 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -108,84 +108,100 @@ static void wake_up_inode(struct inode *inode)
         wake_up_bit(&inode->i_state, __I_LOCK);
 }
 
-static struct inode *alloc_inode(struct super_block *sb)
+/**
+ * inode_init_always - perform inode structure intialisation
+ * @sb          - superblock inode belongs to.
+ * @inode       - inode to initialise
+ *
+ * These are initializations that need to be done on every inode
+ * allocation as the fields are not initialised by slab allocation.
+ */
+struct inode *inode_init_always(struct super_block *sb, struct inode *inode)
 {
         static const struct address_space_operations empty_aops;
         static struct inode_operations empty_iops;
         static const struct file_operations empty_fops;
-        struct inode *inode;
-
-        if (sb->s_op->alloc_inode)
-                inode = sb->s_op->alloc_inode(sb);
-        else
-                inode = (struct inode *) kmem_cache_alloc(inode_cachep, GFP_KERNEL);
 
-        if (inode) {
-                struct address_space * const mapping = &inode->i_data;
-
-                inode->i_sb = sb;
-                inode->i_blkbits = sb->s_blocksize_bits;
-                inode->i_flags = 0;
-                atomic_set(&inode->i_count, 1);
-                inode->i_op = &empty_iops;
-                inode->i_fop = &empty_fops;
-                inode->i_nlink = 1;
-                atomic_set(&inode->i_writecount, 0);
-                inode->i_size = 0;
-                inode->i_blocks = 0;
-                inode->i_bytes = 0;
-                inode->i_generation = 0;
+        struct address_space * const mapping = &inode->i_data;
+
+        inode->i_sb = sb;
+        inode->i_blkbits = sb->s_blocksize_bits;
+        inode->i_flags = 0;
+        atomic_set(&inode->i_count, 1);
+        inode->i_op = &empty_iops;
+        inode->i_fop = &empty_fops;
+        inode->i_nlink = 1;
+        atomic_set(&inode->i_writecount, 0);
+        inode->i_size = 0;
+        inode->i_blocks = 0;
+        inode->i_bytes = 0;
+        inode->i_generation = 0;
 #ifdef CONFIG_QUOTA
-                memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
+        memset(&inode->i_dquot, 0, sizeof(inode->i_dquot));
 #endif
-                inode->i_pipe = NULL;
-                inode->i_bdev = NULL;
-                inode->i_cdev = NULL;
-                inode->i_rdev = 0;
-                inode->dirtied_when = 0;
-                if (security_inode_alloc(inode)) {
-                        if (inode->i_sb->s_op->destroy_inode)
-                                inode->i_sb->s_op->destroy_inode(inode);
-                        else
-                                kmem_cache_free(inode_cachep, (inode));
-                        return NULL;
-                }
+        inode->i_pipe = NULL;
+        inode->i_bdev = NULL;
+        inode->i_cdev = NULL;
+        inode->i_rdev = 0;
+        inode->dirtied_when = 0;
+        if (security_inode_alloc(inode)) {
+                if (inode->i_sb->s_op->destroy_inode)
+                        inode->i_sb->s_op->destroy_inode(inode);
+                else
+                        kmem_cache_free(inode_cachep, (inode));
+                return NULL;
+        }
 
-                spin_lock_init(&inode->i_lock);
-                lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);
+        spin_lock_init(&inode->i_lock);
+        lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);
 
-                mutex_init(&inode->i_mutex);
-                lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_key);
+        mutex_init(&inode->i_mutex);
+        lockdep_set_class(&inode->i_mutex, &sb->s_type->i_mutex_key);
 
-                init_rwsem(&inode->i_alloc_sem);
-                lockdep_set_class(&inode->i_alloc_sem, &sb->s_type->i_alloc_sem_key);
+        init_rwsem(&inode->i_alloc_sem);
+        lockdep_set_class(&inode->i_alloc_sem, &sb->s_type->i_alloc_sem_key);
 
-                mapping->a_ops = &empty_aops;
-                mapping->host = inode;
-                mapping->flags = 0;
-                mapping_set_gfp_mask(mapping, GFP_HIGHUSER_PAGECACHE);
-                mapping->assoc_mapping = NULL;
-                mapping->backing_dev_info = &default_backing_dev_info;
-                mapping->writeback_index = 0;
+        mapping->a_ops = &empty_aops;
+        mapping->host = inode;
+        mapping->flags = 0;
+        mapping_set_gfp_mask(mapping, GFP_HIGHUSER_PAGECACHE);
+        mapping->assoc_mapping = NULL;
+        mapping->backing_dev_info = &default_backing_dev_info;
+        mapping->writeback_index = 0;
 
-                /*
-                 * If the block_device provides a backing_dev_info for client
-                 * inodes then use that.  Otherwise the inode share the bdev's
-                 * backing_dev_info.
-                 */
-                if (sb->s_bdev) {
-                        struct backing_dev_info *bdi;
+        /*
+         * If the block_device provides a backing_dev_info for client
+         * inodes then use that.  Otherwise the inode share the bdev's
+         * backing_dev_info.
+         */
+        if (sb->s_bdev) {
+                struct backing_dev_info *bdi;
 
-                        bdi = sb->s_bdev->bd_inode_backing_dev_info;
-                        if (!bdi)
-                                bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
-                        mapping->backing_dev_info = bdi;
-                }
-                inode->i_private = NULL;
-                inode->i_mapping = mapping;
+                bdi = sb->s_bdev->bd_inode_backing_dev_info;
+                if (!bdi)
+                        bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
+                mapping->backing_dev_info = bdi;
         }
+        inode->i_private = NULL;
+        inode->i_mapping = mapping;
+
         return inode;
 }
+EXPORT_SYMBOL(inode_init_always);
+
+static struct inode *alloc_inode(struct super_block *sb)
+{
+        struct inode *inode;
+
+        if (sb->s_op->alloc_inode)
+                inode = sb->s_op->alloc_inode(sb);
+        else
+                inode = kmem_cache_alloc(inode_cachep, GFP_KERNEL);
+
+        if (inode)
+                return inode_init_always(sb, inode);
+        return NULL;
+}
 
 void destroy_inode(struct inode *inode) 
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5b248d61430c..04abead4b021 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1881,6 +1881,7 @@ extern loff_t default_llseek(struct file *file, loff_t offset, int origin);
 
 extern loff_t vfs_llseek(struct file *file, loff_t offset, int origin);
 
+extern struct inode * inode_init_always(struct super_block *, struct inode *);
 extern void inode_init_once(struct inode *);
 extern void iput(struct inode *);
 extern struct inode * igrab(struct inode *);