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Message-ID: <20081217153940.GA6495@atrey.karlin.mff.cuni.cz>
Date: Wed, 17 Dec 2008 16:39:40 +0100
From: Jan Kara <jack@...e.cz>
To: Theodore Ts'o <tytso@....edu>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
Toshiyuki Okajima <toshi.okajima@...fujitsu.com>,
linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH -v3] vfs: add releasepages hooks to block devices which can be used by file systems
Hello,
> From: Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
>
> 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.
Yes, this is IMO the right fix. I'm just wondering about the fact that we
can't block in the client_releasepage(). That seems to be caused by the fact
that we need to be protected against client_releasepage() callback changes
which essentially means umount, right? I'm not saying I have a better solution
but introducing such limitation seems stupid just because of umount...
Honza
> Signed-off-by: Toshiyuki Okajima <toshi.okajima@...fujitsu.com>
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> Cc: linux-fsdevel@...r.kernel.org
> ---
> 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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--
Jan Kara <jack@...e.cz>
SuSE CR Labs
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