MDP major registration

Neil,

What is the status of the major for the partitionable arrays ?

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

Quoted 3 lines · On Thursday March 13, [email protected] wrote:

Neil,

What is the status of the major for the partitionable arrays ?

automatically determined at runtime.

Quoted 2 lines

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

No. Is there any need?

Quoted 7 lines · Neil Brown

Quoted 3 lines · On Thursday March 13, [email protected] wrote:

Neil,

What is the status of the major for the partitionable arrays ?

automatically determined at runtime.

Quoted 4 lines

Quoted 2 lines

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

No. Is there any need?

I got this question in mind when I saw that mkfs.xfs source code was referring to the MD major to tune its parameters on an MD device, while it ignores MDP devices. If there were reasons to register MD, wouldn't they apply to MDP too ?

Quoted 11 lines · Hubert Verstraete

Quoted 10 lines · Neil Brown

Quoted 3 lines · On Thursday March 13, [email protected] wrote:

Neil,

What is the status of the major for the partitionable arrays ?

automatically determined at runtime.

Quoted 2 lines

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

Quoted 4 lines

Quoted 1 line

No. Is there any need?

I got this question in mind when I saw that mkfs.xfs source code was referring to the MD major to tune its parameters on an MD device, while it ignores MDP devices. If there were reasons to register MD, wouldn't they apply to MDP too ?

i don't think so:
bluca@percy ~ $ grep mdp /proc/devices
253 mdp

Quoted 14 lines · Luca Berra

Quoted 13 lines · Hubert Verstraete

Quoted 11 lines · Neil Brown

Quoted 3 lines · On Thursday March 13, [email protected] wrote:

Neil,

What is the status of the major for the partitionable arrays ?

automatically determined at runtime.

Quoted 2 lines

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

No. Is there any need?

Quoted 6 lines

Quoted 2 lines

I got this question in mind when I saw that mkfs.xfs source code was referring to the MD major to tune its parameters on an MD device, while it ignores MDP devices. If there were reasons to register MD, wouldn't they apply to MDP too ?

i don't think so:
bluca@percy ~ $ grep mdp /proc/devices
253 mdp

Why is it important to have XFS tune its parameters for md and not for mdp? I don't understand your conclusion here, is tuning not needed for mdp, or so meaningless that it doesn't matter, or that XFS code reads /proc/devices, or ??? I note that device-mapper also has a dynamic major, what does XFS make of that?

I don't know how much difference tuning makes, but if it's worth doing at all, it should be done for mdp as well, I would think.

Quoted 15 lines · Bill Davidsen

Quoted 14 lines · Luca Berra

Quoted 13 lines · Hubert Verstraete

Quoted 11 lines · Neil Brown

Quoted 3 lines · On Thursday March 13, [email protected] wrote:

Neil,

What is the status of the major for the partitionable arrays ?

automatically determined at runtime.

Quoted 2 lines

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

No. Is there any need?

Quoted 8 lines

Quoted 6 lines

Quoted 2 lines

I got this question in mind when I saw that mkfs.xfs source code was referring to the MD major to tune its parameters on an MD device, while it ignores MDP devices. If there were reasons to register MD, wouldn't they apply to MDP too ?

i don't think so:
bluca@percy ~ $ grep mdp /proc/devices
253 mdp

Why is it important to have XFS tune its parameters for md and not for mdp? I don't understand your conclusion here, is tuning not needed for mdp, or so meaningless that it doesn't matter, or that XFS code reads /proc/devices, or ??? I note that device-mapper also has a dynamic major, what does XFS make of that?

It reads from /proc/devices.

Quoted 1 line

I don't know how much difference tuning makes, but if it's worth doing at all, it should be done for mdp as well, I would think.

Same thought. I wrote the patch for mkfs.xfs but did not publish it for two reasons:
1) MD is registered but not MDP. Now I understand, it's not a problem, we just need to read /proc/devices as device-mapper does.
2) Tuning XFS for MDP can be achieved through the mkfs.xfs options. With a few lines in shell, my XFS on MDP now has the same performance as XFS on MD.

Hubert

Signature · 3 lines

To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to [email protected]
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Hi XFS list,

please find attached a patch for libdisk/mkfs.xfs which tunes XFS on software partitionable RAID arrays, also called mdp.

Hubert Verstraete

------------------------------------------------------------------------

diff -u -r xfsprogs-2.8.11/libdisk/md.c xfsprogs-2.8.11-mdp/libdisk/md.c

libdisk/md.c +30 -5

@@ -24,8 +24,12 @@
 	dev_t		dev)
 {
 	if (major(dev) == MD_MAJOR)
-		return 1;
-	return get_driver_block_major("md", major(dev));
+		return MD_IS_MD;
+	if (get_driver_block_major("md", major(dev)))
+		return MD_IS_MD;
+	if (get_driver_block_major("mdp", major(dev)))
+		return MD_IS_MDP;
+	return 0;
 }
 
 int

@@ -37,12 +41,32 @@
 	int		*sectalign,
 	struct stat64	*sb)
 {
-	if (mnt_is_md_subvol(sb->st_rdev)) {
+	char *pc, *dfile2 = NULL;
+	int is_md;
+
+	if ((is_md = mnt_is_md_subvol(sb->st_rdev))) {
 		struct md_array_info	md;
 		int			fd;
 
+		if (is_md == MD_IS_MDP) {
+			if (!(pc = strrchr(dfile, 'd'))
+			|| !(pc = strchr(pc, 'p'))) {
+				fprintf(stderr,
+					_("Error getting MD array device from %s\n"),
+					dfile);
+				exit(1);
+			}
+			dfile2 = (char *) malloc(pc - dfile + 1);
+			if (dfile2 == NULL) {
+				fprintf(stderr,
+					_("Couldn't malloc device string\n"));
+				exit(1);
+			}
+			strncpy(dfile2, dfile, pc - dfile);
+			dfile2[pc - dfile + 1] = '\0';
+		}
 		/* Open device */
-		fd = open(dfile, O_RDONLY);
+		fd = open(dfile2 ? dfile2 : dfile, O_RDONLY);
 		if (fd == -1)
 			return 0;
 

@@ -50,10 +74,11 @@
 		if (ioctl(fd, GET_ARRAY_INFO, &md)) {
 			fprintf(stderr,
 				_("Error getting MD array info from %s\n"),
-				dfile);
+				dfile2 ? dfile2 : dfile);
 			exit(1);
 		}
 		close(fd);
+		if (dfile2) free(dfile2);
 
 		/*
 		 * Ignore levels we don't want aligned (e.g. linear)

diff -u -r xfsprogs-2.8.11/libdisk/md.h xfsprogs-2.8.11-mdp/libdisk/md.h

libdisk/md.h +3 -0

@@ -20,6 +20,9 @@
 #define MD_MAJOR		9 /* we also check at runtime */
 #endif
 
+#define MD_IS_MD		1
+#define MD_IS_MDP		2
+
 #define GET_ARRAY_INFO          _IOR (MD_MAJOR, 0x11, struct md_array_info)
 
 #define MD_SB_CLEAN		0

The line 89 in libdisk/md.c is: "free(dfile2);" but it should have remained "if (dfile2) free(dfile2);" because dfile2 is null in case mkfs.xfs is run on an MD device.

Quoted 15 lines · Bill Davidsen

Quoted 14 lines · Luca Berra

Quoted 13 lines · Hubert Verstraete

Quoted 11 lines · Neil Brown

Quoted 3 lines · On Thursday March 13, [email protected] wrote:

Neil,

What is the status of the major for the partitionable arrays ?

automatically determined at runtime.

Quoted 2 lines

I see that it is 254, which is in the experimental section, according to the official Linux device list (http://www.lanana.org/docs/device-list/).
Will there be an official registration ?

No. Is there any need?

Quoted 8 lines

Quoted 6 lines

Quoted 2 lines

I got this question in mind when I saw that mkfs.xfs source code was referring to the MD major to tune its parameters on an MD device, while it ignores MDP devices. If there were reasons to register MD, wouldn't they apply to MDP too ?

i don't think so:
bluca@percy ~ $ grep mdp /proc/devices
253 mdp

Why is it important to have XFS tune its parameters for md and not for mdp? I don't understand your conclusion here, is tuning not needed for mdp, or so meaningless that it doesn't matter, or that XFS code reads /proc/devices, or ??? I note that device-mapper also has a dynamic major, what does XFS make of that?

It reads from /proc/devices.

Quoted 1 line

I don't know how much difference tuning makes, but if it's worth doing at all, it should be done for mdp as well, I would think.

Same thought. I wrote the patch for mkfs.xfs but did not publish it for two reasons:
1) MD is registered but not MDP. Now I understand, it's not a problem, we just need to read /proc/devices as device-mapper does.
2) Tuning XFS for MDP can be achieved through the mkfs.xfs options. With a few lines in shell, my XFS on MDP now has the same performance as XFS on MD.