block: look up block device path in sysfs

PATCH In review Dan Williams 2 participants 3 messages Jan 26, 2008 – Jan 28, 2008

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VFS Block layer

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Dan Williams

author

2008-01-26 05:05 UTC #0 lore raw

PATCH 1/1 block: look up block device path in sysfs

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 <[email protected]>

Cc Neil Brown <[email protected]>

Cc Kay Sievers <[email protected]>

Signed-off-by Dan Williams <[email protected]>

---
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(-)

block/compat_ioctl.c +1 -0

index cae0a85..d71d287 100644
@@ -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:
 	/*

block/ioctl.c +28 -0

index 52d6385..d048ae4 100644
@@ -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;

include/linux/fs.h +1 -0

index b3ec4a4..b4cf8f3 100644
@@ -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 */

Christoph Hellwig

2008-01-26 20:23 UTC #1 lore raw

Quoted 9 lines · 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.

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

Dan Williams

author

2008-01-28 18:45 UTC #2 lore raw

Quoted 5 lines · Christoph Hellwig

Quoted 4 lines · Dan Williams
Given an fd on a block device, returns a string like
      /block/sda/sda1

Quoted 8 lines

Quoted 5 lines
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