From: Toshiyuki Okajima <toshi.okajima@xxxxxxxxxxxxxx>
Implement blkdev_releasepage() to release the buffer_heads and page
after we release private data which belongs to a client of the block
device, such as a filesystem.
blkdev_releasepage() call the client's releasepage() which is
registered by blkdev_register_client_releasepage() to release its
private data.
Signed-off-by: Toshiyuki Okajima <toshi.okajima@xxxxxxxxxxxxxx>
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
---
fs/block_dev.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/super.c | 22 ++++++++++++++++
include/linux/fs.h | 9 +++++++
3 files changed, 99 insertions(+), 0 deletions(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index db831ef..bac0a38 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -29,6 +29,9 @@
struct bdev_inode {
struct block_device bdev;
+ void *client;
+ int (*client_releasepage)(void*, struct page*, gfp_t);
+ rwlock_t client_lock;
struct inode vfs_inode;
};
@@ -260,6 +263,9 @@ static struct inode *bdev_alloc_inode(struct super_block *sb)
struct bdev_inode *ei = kmem_cache_alloc(bdev_cachep, GFP_KERNEL);
if (!ei)
return NULL;
+ ei->client = NULL;
+ ei->client_releasepage = NULL;
+ rwlock_init(&ei->client_lock);
return &ei->vfs_inode;
}
@@ -1208,6 +1214,67 @@ static long block_ioctl(struct file *file, unsigned cmd, unsigned long arg)
return blkdev_ioctl(bdev, mode, cmd, arg);
}
+/*
+ * blkdev_releasepage: execute ei->client_releasepage() if it exists.
+ * Otherwise, execute try_to_free_buffers().
+ * ei->client_releasepage() releases private client's page if possible.
+ * Because a buffer_head's using counter is bigger than 0 if a client has
+ * a page for private usage. If so, try_to_free_buffers() cannot release it.
+ * Therefore a client must try to release a page itself.
+ */
+static int blkdev_releasepage(struct page *page, gfp_t wait)
+{
+ struct bdev_inode *ei = BDEV_I(page->mapping->host);
+ int ret;
+
+ read_lock(&ei->client_lock);
+ if (ei->client_releasepage != NULL)
+ /*
+ * Since we are holding a spinlock (ei->client_lock),
+ * make sure the client_releasepage function
+ * understands that it must not block.
+ */
+ ret = (*ei->client_releasepage)(ei->client, page,
+ wait & ~__GFP_WAIT);
+ else
+ ret = try_to_free_buffers(page);
+ read_unlock(&ei->client_lock);
+ return ret;
+}
+
+/*
+ * blkdev_register_client_releasepage: register client_releasepage.
+ */
+int blkdev_register_client_releasepage(struct block_device *bdev,
+ void *client, int (*releasepage)(void*, struct page*, gfp_t))
+{
+ struct bdev_inode *ei = BDEV_I(bdev->bd_inode);
+ int ret = 1;
+
+ write_lock(&ei->client_lock);
+ if (ei->client == NULL && ei->client_releasepage == NULL) {
+ ei->client = client;
+ ei->client_releasepage = releasepage;
+ } else if (ei->client != client
+ || ei->client_releasepage != releasepage)
+ ret = 0;
+ write_unlock(&ei->client_lock);
+ return ret;
+}
+
+/*
+ * blkdev_unregister_client_releasepage: unregister client_releasepage.
+ */
+void blkdev_unregister_client_releasepage(struct block_device *bdev)
+{
+ struct bdev_inode *ei = BDEV_I(bdev->bd_inode);
+
+ write_lock(&ei->client_lock);
+ ei->client = NULL;
+ ei->client_releasepage = NULL;
+ write_unlock(&ei->client_lock);
+}
+
static const struct address_space_operations def_blk_aops = {
.readpage = blkdev_readpage,
.writepage = blkdev_writepage,
@@ -1215,6 +1282,7 @@ static const struct address_space_operations def_blk_aops = {
.write_begin = blkdev_write_begin,
.write_end = blkdev_write_end,
.writepages = generic_writepages,
+ .releasepage = blkdev_releasepage,
.direct_IO = blkdev_direct_IO,
};
diff --git a/fs/super.c b/fs/super.c
index 400a760..fd254eb 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -801,6 +801,18 @@ int get_sb_bdev(struct file_system_type *fs_type,
s->s_flags |= MS_ACTIVE;
}
+ /*
+ * register a client function which releases a page whose mapping is
+ * block device
+ */
+ if (fs_type->release_metadata != NULL
+ && !blkdev_register_client_releasepage(bdev, s,
+ fs_type->release_metadata)) {
+ up_write(&s->s_umount);
+ deactivate_super(s);
+ error = -EBUSY;
+ goto error_bdev;
+ }
return simple_set_mnt(mnt, s);
@@ -819,6 +831,16 @@ void kill_block_super(struct super_block *sb)
struct block_device *bdev = sb->s_bdev;
fmode_t mode = sb->s_mode;
+ /*
+ * unregister a client function which releases a page whose mapping is
+ * block device
+ *
+ * This is sure to be unmounting here, and it releases all own data
+ * itself. Therefore the filesystem's function which is owned by the
+ * block device, which releases its data is not needed any more.
+ */
+ if (sb->s_type->release_metadata != NULL)
+ blkdev_unregister_client_releasepage(bdev);
generic_shutdown_super(sb);
sync_blockdev(bdev);
close_bdev_exclusive(bdev, mode);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0dcdd94..398c8ed 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1538,6 +1538,7 @@ struct file_system_type {
int (*get_sb) (struct file_system_type *, int,
const char *, void *, struct vfsmount *);
void (*kill_sb) (struct super_block *);
+ int (*release_metadata)(void*, struct page*, gfp_t);
struct module *owner;
struct file_system_type * next;
struct list_head fs_supers;
@@ -1699,8 +1700,16 @@ extern void bd_set_size(struct block_device *, loff_t size);
extern void bd_forget(struct inode *inode);
extern void bdput(struct block_device *);
extern struct block_device *open_by_devnum(dev_t, fmode_t);
+extern int blkdev_register_client_releasepage(struct block_device *,
+ void *, int (*releasepage)(void *, struct page*, gfp_t));
+extern void blkdev_unregister_client_releasepage(struct block_device *);
#else
static inline void bd_forget(struct inode *inode) {}
+static inline int blkdev_register_client_releasepage(struct block_device *,
+ void *, int (*releasepage)(void *, struct page*, gfp_t))
+{ return 1; }
+static inline void blkdev_unregister_client_releasepage(struct block_device *)
+{}
#endif
extern const struct file_operations def_blk_fops;
extern const struct file_operations def_chr_fops;
--
1.6.0.4.8.g36f27.dirty
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