Re: [PATCH] osdblk: a Linux block device for OSD objects

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James Bottomley wrote:
+   1) Map a Linux block device to an existing OSD object.
+
+      In this example, we will use partition id 1234, object id 5678,
+      OSD device /dev/osd1.
+
+      $ echo "1234 5678 /dev/osd1" > /sys/class/osdblk/add
+
+
+   2) List all active blkdev<->object mappings.
+
+      In this example, we have performed step #1 twice, creating two blkdevs,
+      mapped to two separate OSD objects.
+
+      $ cat /sys/class/osdblk/list
+      0 174 1234 5678 /dev/osd1
+      1 179 1994 897123 /dev/osd0

This is a slight violation of the one piece of data per sysfs file
rule ... might it not be better as a file named <partid>-<objid> linking
to the osd device location in sysfs?

Yeah... I leaned more towards a consolidated table, as it was elegantly implemented in just a few lines of code, including locking :)


+      The columns, in order, are:
+      - blkdev unique id
+      - blkdev assigned major
+      - OSD object partition id
+      - OSD object id
+      - OSD device
+
+
+   3) Remove an active blkdev<->object mapping.
+


+	unsigned long		obj_id;
+	char			osd_path[0];
+};
+
+static struct class *class_osdblk;		/* /sys/class/osdblk */
+static struct mutex ctl_mutex;	/* Serialize open/close/setup/teardown */
+static struct osdblk_device *osdblk_devs[OSDBLK_MAX_DEVS];

Might it not be better to do this as a linked list on the private dev
structure instead?  This only works if you have one entry
in /sys/class/osdblock per device because now you have a device private
pointer to hang it off

converted to list



+static int osdblk_get_free_req(struct osdblk_device *osdev)
+{
+	int i;
+
+	for (i = 0; i < OSDBLK_MAX_REQ; i++) {
+		if (!osdev->req[i].rq)
+			return i;
+	}

Rather than using a static list of outstanding requests, I think you
could probably use the block tag handling infrastructure for all of this

converted to use blk-tag.c gadgetry

Thanks for the review!

	Jeff


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