diff mbox series

[01/32] block: Provide blkdev_get_handle_* functions

Message ID 20230704122224.16257-1-jack@suse.cz
State New
Headers show
Series block: Make blkdev_get_by_*() return handle | expand

Commit Message

Jan Kara July 4, 2023, 12:21 p.m. UTC
Create struct bdev_handle that contains all parameters that need to be
passed to blkdev_put() and provide blkdev_get_handle_* functions that
return this structure instead of plain bdev pointer. This will
eventually allow us to pass one more argument to blkdev_put() without
too much hassle.

CC: Alasdair Kergon <agk@redhat.com>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Anna Schumaker <anna@kernel.org>
CC: Chao Yu <chao@kernel.org>
CC: Christian Borntraeger <borntraeger@linux.ibm.com>
CC: Coly Li <colyli@suse.de
CC: "Darrick J. Wong" <djwong@kernel.org>
CC: Dave Kleikamp <shaggy@kernel.org>
CC: David Sterba <dsterba@suse.com>
CC: dm-devel@redhat.com
CC: drbd-dev@lists.linbit.com
CC: Gao Xiang <xiang@kernel.org>
CC: Jack Wang <jinpu.wang@ionos.com>
CC: Jaegeuk Kim <jaegeuk@kernel.org>
CC: jfs-discussion@lists.sourceforge.net
CC: Joern Engel <joern@lazybastard.org>
CC: Joseph Qi <joseph.qi@linux.alibaba.com>
CC: Kent Overstreet <kent.overstreet@gmail.com>
CC: linux-bcache@vger.kernel.org
CC: linux-btrfs@vger.kernel.org
CC: linux-erofs@lists.ozlabs.org
CC: <linux-ext4@vger.kernel.org>
CC: linux-f2fs-devel@lists.sourceforge.net
CC: linux-mm@kvack.org
CC: linux-mtd@lists.infradead.org
CC: linux-nfs@vger.kernel.org
CC: linux-nilfs@vger.kernel.org
CC: linux-nvme@lists.infradead.org
CC: linux-pm@vger.kernel.org
CC: linux-raid@vger.kernel.org
CC: linux-s390@vger.kernel.org
CC: linux-scsi@vger.kernel.org
CC: linux-xfs@vger.kernel.org
CC: "Md. Haris Iqbal" <haris.iqbal@ionos.com>
CC: Mike Snitzer <snitzer@kernel.org>
CC: Minchan Kim <minchan@kernel.org>
CC: ocfs2-devel@oss.oracle.com
CC: reiserfs-devel@vger.kernel.org
CC: Sergey Senozhatsky <senozhatsky@chromium.org>
CC: Song Liu <song@kernel.org>
CC: Sven Schnelle <svens@linux.ibm.com>
CC: target-devel@vger.kernel.org
CC: Ted Tso <tytso@mit.edu>
CC: Trond Myklebust <trond.myklebust@hammerspace.com>
CC: xen-devel@lists.xenproject.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 block/bdev.c           | 47 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h | 10 +++++++++
 2 files changed, 57 insertions(+)

Comments

Jan Kara July 5, 2023, 4:12 p.m. UTC | #1
On Tue 04-07-23 07:06:26, Bart Van Assche wrote:
> On 7/4/23 05:21, Jan Kara wrote:
> > +struct bdev_handle {
> > +	struct block_device *bdev;
> > +	void *holder;
> > +};
> 
> Please explain in the patch description why a holder pointer is introduced
> in struct bdev_handle and how it relates to the bd_holder pointer in struct
> block_device. Is one of the purposes of this patch series perhaps to add
> support for multiple holders per block device?

No. The reason for adding holder to struct bdev_handle is that it is an
argument blkdev_put() needs. Currently, every user of blkdev_put() has to
remember what it has passed as 'holder' to blkdev_get_by_*() call and pass
that to blkdev_put(). With struct bdev_handle this will happen
automatically. This is already explained in the changelog of this patch:

"Create struct bdev_handle that contains all parameters that need to be
passed to blkdev_put()..."

If it was only about holder, the intrusive patches would not be warranted
but as the description also says:

"This will eventually allow us to pass one more argument to blkdev_put()
without too much hassle."

Because we will additionaly need to propagate the 'mode' argument used at
open to blkdev_put().

								Honza
Christoph Hellwig July 6, 2023, 3:38 p.m. UTC | #2
On Tue, Jul 04, 2023 at 02:21:28PM +0200, Jan Kara wrote:
> Create struct bdev_handle that contains all parameters that need to be
> passed to blkdev_put() and provide blkdev_get_handle_* functions that
> return this structure instead of plain bdev pointer. This will
> eventually allow us to pass one more argument to blkdev_put() without
> too much hassle.

Can we use the opportunity to come up with better names?  blkdev_get_*
was always a rather horrible naming convention for something that
ends up calling into ->open.

What about:

struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
		const struct blk_holder_ops *hops);
struct bdev_handle *bdev_open_by_path(dev_t dev, blk_mode_t mode,
		void *holder, const struct blk_holder_ops *hops);
void bdev_release(struct bdev_handle *handle);

?
Jan Kara July 6, 2023, 4:14 p.m. UTC | #3
On Thu 06-07-23 08:38:40, Christoph Hellwig wrote:
> On Tue, Jul 04, 2023 at 02:21:28PM +0200, Jan Kara wrote:
> > Create struct bdev_handle that contains all parameters that need to be
> > passed to blkdev_put() and provide blkdev_get_handle_* functions that
> > return this structure instead of plain bdev pointer. This will
> > eventually allow us to pass one more argument to blkdev_put() without
> > too much hassle.
> 
> Can we use the opportunity to come up with better names?  blkdev_get_*
> was always a rather horrible naming convention for something that
> ends up calling into ->open.
> 
> What about:
> 
> struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
> 		const struct blk_holder_ops *hops);
> struct bdev_handle *bdev_open_by_path(dev_t dev, blk_mode_t mode,
> 		void *holder, const struct blk_holder_ops *hops);
> void bdev_release(struct bdev_handle *handle);

I'd maybe use bdev_close() instead of bdev_release() but otherwise I like
the new naming.

								Honza
Christoph Hellwig July 7, 2023, 11:28 a.m. UTC | #4
On Thu, Jul 06, 2023 at 06:14:33PM +0200, Jan Kara wrote:
> > struct bdev_handle *bdev_open_by_path(dev_t dev, blk_mode_t mode,
> > 		void *holder, const struct blk_holder_ops *hops);
> > void bdev_release(struct bdev_handle *handle);
> 
> I'd maybe use bdev_close() instead of bdev_release() but otherwise I like
> the new naming.

We're using release everywhese else, but if Jens is fine with that I
can live with close.
Jan Kara July 7, 2023, 12:24 p.m. UTC | #5
On Fri 07-07-23 04:28:41, Christoph Hellwig wrote:
> On Thu, Jul 06, 2023 at 06:14:33PM +0200, Jan Kara wrote:
> > > struct bdev_handle *bdev_open_by_path(dev_t dev, blk_mode_t mode,
> > > 		void *holder, const struct blk_holder_ops *hops);
> > > void bdev_release(struct bdev_handle *handle);
> > 
> > I'd maybe use bdev_close() instead of bdev_release() but otherwise I like
> > the new naming.
> 
> We're using release everywhese else, but if Jens is fine with that I
> can live with close.

Dunno, to me words pair like open-close, get-put, acquire-release.
Furthermore e.g. ->release() (and thus blkdev_release()) is called only
when the last file reference is dropped, not when each reference is
dropped, so that's why bdev_release() seems a bit confusing to me.

								Honza
Haris Iqbal July 12, 2023, 4:06 p.m. UTC | #6
On Thu, Jul 6, 2023 at 5:38 PM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Tue, Jul 04, 2023 at 02:21:28PM +0200, Jan Kara wrote:
> > Create struct bdev_handle that contains all parameters that need to be
> > passed to blkdev_put() and provide blkdev_get_handle_* functions that
> > return this structure instead of plain bdev pointer. This will
> > eventually allow us to pass one more argument to blkdev_put() without
> > too much hassle.
>
> Can we use the opportunity to come up with better names?  blkdev_get_*
> was always a rather horrible naming convention for something that
> ends up calling into ->open.
>
> What about:
>
> struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
>                 const struct blk_holder_ops *hops);
> struct bdev_handle *bdev_open_by_path(dev_t dev, blk_mode_t mode,
>                 void *holder, const struct blk_holder_ops *hops);
> void bdev_release(struct bdev_handle *handle);

+1 to this.
Also, if we are removing "handle" from the function, should the name
of the structure it returns also change? Would something like bdev_ctx
be better?

(Apologies for the previous non-plaintext email)

>
> ?
Jan Kara July 31, 2023, 10:50 a.m. UTC | #7
On Wed 12-07-23 18:06:35, Haris Iqbal wrote:
> On Thu, Jul 6, 2023 at 5:38 PM Christoph Hellwig <hch@infradead.org> wrote:
> >
> > On Tue, Jul 04, 2023 at 02:21:28PM +0200, Jan Kara wrote:
> > > Create struct bdev_handle that contains all parameters that need to be
> > > passed to blkdev_put() and provide blkdev_get_handle_* functions that
> > > return this structure instead of plain bdev pointer. This will
> > > eventually allow us to pass one more argument to blkdev_put() without
> > > too much hassle.
> >
> > Can we use the opportunity to come up with better names?  blkdev_get_*
> > was always a rather horrible naming convention for something that
> > ends up calling into ->open.
> >
> > What about:
> >
> > struct bdev_handle *bdev_open_by_dev(dev_t dev, blk_mode_t mode, void *holder,
> >                 const struct blk_holder_ops *hops);
> > struct bdev_handle *bdev_open_by_path(dev_t dev, blk_mode_t mode,
> >                 void *holder, const struct blk_holder_ops *hops);
> > void bdev_release(struct bdev_handle *handle);
> 
> +1 to this.
> Also, if we are removing "handle" from the function, should the name
> of the structure it returns also change? Would something like bdev_ctx
> be better?

I think the bdev_handle name is fine for the struct. After all it is
equivalent of an open handle for the block device so IMHO bdev_handle
captures that better than bdev_ctx.

								Honza
Christoph Hellwig July 31, 2023, 11:13 a.m. UTC | #8
On Mon, Jul 31, 2023 at 12:50:34PM +0200, Jan Kara wrote:
> I think the bdev_handle name is fine for the struct. After all it is
> equivalent of an open handle for the block device so IMHO bdev_handle
> captures that better than bdev_ctx.

Agreed.
diff mbox series

Patch

diff --git a/block/bdev.c b/block/bdev.c
index 979e28a46b98..c75de5cac2bc 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -846,6 +846,24 @@  struct block_device *blkdev_get_by_dev(dev_t dev, blk_mode_t mode, void *holder,
 }
 EXPORT_SYMBOL(blkdev_get_by_dev);
 
+struct bdev_handle *blkdev_get_handle_by_dev(dev_t dev, blk_mode_t mode,
+		void *holder, const struct blk_holder_ops *hops)
+{
+	struct bdev_handle *handle = kmalloc(sizeof(struct bdev_handle),
+					     GFP_KERNEL);
+	struct block_device *bdev;
+
+	if (!handle)
+		return ERR_PTR(-ENOMEM);
+	bdev = blkdev_get_by_dev(dev, mode, holder, hops);
+	if (IS_ERR(bdev))
+		return ERR_CAST(bdev);
+	handle->bdev = bdev;
+	handle->holder = holder;
+	return handle;
+}
+EXPORT_SYMBOL(blkdev_get_handle_by_dev);
+
 /**
  * blkdev_get_by_path - open a block device by name
  * @path: path to the block device to open
@@ -884,6 +902,28 @@  struct block_device *blkdev_get_by_path(const char *path, blk_mode_t mode,
 }
 EXPORT_SYMBOL(blkdev_get_by_path);
 
+struct bdev_handle *blkdev_get_handle_by_path(const char *path, blk_mode_t mode,
+		void *holder, const struct blk_holder_ops *hops)
+{
+	struct bdev_handle *handle;
+	dev_t dev;
+	int error;
+
+	error = lookup_bdev(path, &dev);
+	if (error)
+		return ERR_PTR(error);
+
+	handle = blkdev_get_handle_by_dev(dev, mode, holder, hops);
+	if (!IS_ERR(handle) && (mode & BLK_OPEN_WRITE) &&
+	    bdev_read_only(handle->bdev)) {
+		blkdev_handle_put(handle);
+		return ERR_PTR(-EACCES);
+	}
+
+	return handle;
+}
+EXPORT_SYMBOL(blkdev_get_handle_by_path);
+
 void blkdev_put(struct block_device *bdev, void *holder)
 {
 	struct gendisk *disk = bdev->bd_disk;
@@ -920,6 +960,13 @@  void blkdev_put(struct block_device *bdev, void *holder)
 }
 EXPORT_SYMBOL(blkdev_put);
 
+void blkdev_handle_put(struct bdev_handle *handle)
+{
+	blkdev_put(handle->bdev, handle->holder);
+	kfree(handle);
+}
+EXPORT_SYMBOL(blkdev_handle_put);
+
 /**
  * lookup_bdev() - Look up a struct block_device by name.
  * @pathname: Name of the block device in the filesystem.
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index ed44a997f629..a910e9997ddd 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1471,14 +1471,24 @@  struct blk_holder_ops {
 #define sb_open_mode(flags) \
 	(BLK_OPEN_READ | (((flags) & SB_RDONLY) ? 0 : BLK_OPEN_WRITE))
 
+struct bdev_handle {
+	struct block_device *bdev;
+	void *holder;
+};
+
 struct block_device *blkdev_get_by_dev(dev_t dev, blk_mode_t mode, void *holder,
 		const struct blk_holder_ops *hops);
 struct block_device *blkdev_get_by_path(const char *path, blk_mode_t mode,
 		void *holder, const struct blk_holder_ops *hops);
+struct bdev_handle *blkdev_get_handle_by_dev(dev_t dev, blk_mode_t mode,
+		void *holder, const struct blk_holder_ops *hops);
+struct bdev_handle *blkdev_get_handle_by_path(const char *path, blk_mode_t mode,
+		void *holder, const struct blk_holder_ops *hops);
 int bd_prepare_to_claim(struct block_device *bdev, void *holder,
 		const struct blk_holder_ops *hops);
 void bd_abort_claiming(struct block_device *bdev, void *holder);
 void blkdev_put(struct block_device *bdev, void *holder);
+void blkdev_handle_put(struct bdev_handle *handle);
 
 /* just for blk-cgroup, don't use elsewhere */
 struct block_device *blkdev_get_no_open(dev_t dev);