[PATCH] block: look up block device path in sysfs

[PATCH] block: look up block device path in sysfs

[Dan Williams]

Given an fd on a block device, returns a string like

	/block/sda/sda1

which can be used to find related information in /sys.

Ideally we should have an ioctl that works on char devices as well,
but that seems far from trivial, so it seems reasonable to have
this until the latter can be implemented.

Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Things have been quiet since this was posted about a month ago, and I am
hoping to see this in 2.6.25.  It is based on Neil's BLKGETNAME patch
and is updated with Kay's comments.

Regards,
Dan

 block/compat_ioctl.c |    1 +
 block/ioctl.c        |   28 ++++++++++++++++++++++++++++
 include/linux/fs.h   |    1 +
 3 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index cae0a85..d71d287 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -784,6 +784,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 	switch (cmd) {
 	case HDIO_GETGEO:
 		return compat_hdio_getgeo(disk, bdev, compat_ptr(arg));
+	case BLKGETDEVPATH:
 	case BLKFLSBUF:
 	case BLKROSET:
 	/*
diff --git a/block/ioctl.c b/block/ioctl.c
index 52d6385..d048ae4 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -229,6 +229,34 @@ int blkdev_ioctl(struct inode *inode, struct file *file, unsigned cmd,
 	int ret, n;
 
 	switch(cmd) {
+	case BLKGETDEVPATH: {
+		char *path;
+		char b[BDEVNAME_SIZE];
+		size_t len;
+
+		path = kobject_get_path(&disk->kobj, GFP_KERNEL);
+
+		if (!path)
+			return -ENOMEM;
+
+		len = strlen(path);
+		if (copy_to_user((char __user *)arg, path, len + 1)) {
+			kfree(path);
+			return -EFAULT;
+		}
+		kfree(path);
+
+		if (bdev->bd_contains == bdev)
+			return 0;
+
+		bdevname(bdev, b);
+		if (copy_to_user((char __user *)arg + len, "/", 2))
+			return -EFAULT;
+		if (copy_to_user((char __user *)arg + len + 1, b,
+				 strlen(b) + 1))
+			return -EFAULT;
+		return 0;
+	}
 	case BLKFLSBUF:
 		if (!capable(CAP_SYS_ADMIN))
 			return -EACCES;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b3ec4a4..b4cf8f3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -217,6 +217,7 @@ extern int dir_notify_enable;
 #define BLKTRACESTART _IO(0x12,116)
 #define BLKTRACESTOP _IO(0x12,117)
 #define BLKTRACETEARDOWN _IO(0x12,118)
+#define BLKGETDEVPATH _IOR(0x12, 119, char [1024])
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */

Re: [PATCH] block: look up block device path in sysfs

[Christoph Hellwig]

On Fri, Jan 25, 2008 at 10:04:51PM -0700, Dan Williams wrote:
> Given an fd on a block device, returns a string like
> 
> 	/block/sda/sda1
> 
> which can be used to find related information in /sys.
> 
> Ideally we should have an ioctl that works on char devices as well,
> but that seems far from trivial, so it seems reasonable to have
> this until the latter can be implemented.

What did you do to address Viro's reasonable rejection of this when
it came up last time?

Re: [PATCH] block: look up block device path in sysfs

[Dan Williams]

On Sat, 2008-01-26 at 13:22 -0700, Christoph Hellwig wrote:
> On Fri, Jan 25, 2008 at 10:04:51PM -0700, Dan Williams wrote:
> > Given an fd on a block device, returns a string like
> >
> >       /block/sda/sda1
> >
> > which can be used to find related information in /sys.
> >
> > Ideally we should have an ioctl that works on char devices as well,
> > but that seems far from trivial, so it seems reasonable to have
> > this until the latter can be implemented.
> 
> What did you do to address Viro's reasonable rejection of this when
> it came up last time?

What was the objection?

My search only came up with a discussion about possibly making this a
generic capability for all devices:
http://marc.info/?t=118646704500006&r=1&w=2

Regards,
Dan