[PATCH RFC] brd: Add miscdevice to control creation and deletion of ramdisks
From: Hannes Frederic Sowa
Date: Sat Oct 13 2012 - 22:53:50 EST
While toying around with a library which needs small block devices for
quorum management, I came up with this small patch to dynamically create
and destroy ram disks (I wanted to have non-swappable backed devices).
I am not really comfortable with the the double-use of the ioctl parameter
of BRD_CTL_ADD passing the size and returning the minor id. But it seemed
the easiest way to go. I even don't know if going the ioctl-route is
the right way.
Currently new minor ids are allocated strictly sequential. Deleted ones
won't get reused. If the ioctl way is the way to go, I may change the
bookkeeping to idrs. Feedback appreciated!
This patch is against 3.6.
This patch adds the miscdevice /dev/brd-control with two ioctls:
1) BRD_CTL_ADD: Instantiates a new ram disk with a given size as
parameter. This parameter is filled in with the new minor id
on return.
2) BRD_CTL_DEL: Deletes a ram disk. Takes the minor id as parameter.
Signed-off-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
---
Documentation/ioctl/ioctl-number.txt | 1 +
drivers/block/brd.c | 115 ++++++++++++++++++++++++++++++++---
include/linux/Kbuild | 1 +
include/linux/brd.h | 11 ++++
include/linux/miscdevice.h | 1 +
5 files changed, 122 insertions(+), 7 deletions(-)
create mode 100644 include/linux/brd.h
diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 849b771..b8827eb 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -326,4 +326,5 @@ Code Seq#(hex) Include File Comments
<mailto:raph@xxxxxx>
0xF6 all LTTng Linux Trace Toolkit Next Generation
<mailto:mathieu.desnoyers@xxxxxxxxxxxx>
+0xF7 00-01 drivers/block/brd.c block ram device control driver
0xFD all linux/dm-ioctl.h
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 531ceb3..7401de7 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -19,6 +19,9 @@
#include <linux/radix-tree.h>
#include <linux/fs.h>
#include <linux/slab.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/brd.h>
#include <asm/uaccess.h>
@@ -460,7 +463,7 @@ __setup("ramdisk_size=", ramdisk_size);
static LIST_HEAD(brd_devices);
static DEFINE_MUTEX(brd_devices_mutex);
-static struct brd_device *brd_alloc(int i)
+static struct brd_device *brd_alloc(int i, int size_kb)
{
struct brd_device *brd;
struct gendisk *disk;
@@ -494,7 +497,7 @@ static struct brd_device *brd_alloc(int i)
disk->queue = brd->brd_queue;
disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
sprintf(disk->disk_name, "ram%d", i);
- set_capacity(disk, rd_size * 2);
+ set_capacity(disk, size_kb * 2);
return brd;
@@ -523,7 +526,7 @@ static struct brd_device *brd_init_one(int i)
goto out;
}
- brd = brd_alloc(i);
+ brd = brd_alloc(i, rd_size);
if (brd) {
add_disk(brd->brd_disk);
list_add_tail(&brd->brd_list, &brd_devices);
@@ -553,9 +556,97 @@ static struct kobject *brd_probe(dev_t dev, int *part, void *data)
return kobj;
}
+static long brd_control_ioctl(struct file *file, unsigned int cmd,
+ unsigned long param)
+{
+ int error = -ENOSYS;
+ int size_kb, val;
+ struct brd_device *brd, *brd2;
+
+ if (rd_nr)
+ return -EINVAL;
+
+ mutex_lock(&brd_devices_mutex);
+ switch (cmd) {
+ case BRD_CTL_ADD:
+ error = get_user(size_kb, (int __user *)param);
+ if (error < 0)
+ break;
+ if (size_kb < 0) {
+ error = -EINVAL;
+ break;
+ }
+ val = 0;
+ list_for_each_entry(brd, &brd_devices, brd_list) {
+ val = max(val, 1 + brd->brd_number);
+ }
+ if (val >= (MINORMASK >> part_shift)) {
+ error = -EINVAL;
+ break;
+ }
+ brd = brd_alloc(val, size_kb);
+ if (brd == NULL) {
+ error = -ENOMEM;
+ break;
+ }
+ list_add_tail(&brd->brd_list, &brd_devices);
+ add_disk(brd->brd_disk);
+ val <<= part_shift;
+ error = put_user(val, (int __user *)param);
+ if (error < 0)
+ break;
+ error = 0;
+ break;
+ case BRD_CTL_DEL:
+ error = get_user(val, (int __user *)param);
+ if (error < 0)
+ break;
+ if ((val & max_part) != 0) {
+ error = -EINVAL;
+ break;
+ }
+ val >>= part_shift;
+ brd2 = NULL;
+ list_for_each_entry(brd, &brd_devices, brd_list) {
+ if (brd->brd_number == val) {
+ brd2 = brd;
+ break;
+ }
+ }
+ if (brd2 == NULL) {
+ error = -ENODEV;
+ break;
+ }
+ brd_del_one(brd2);
+ break;
+ }
+ mutex_unlock(&brd_devices_mutex);
+ return error;
+}
+
+static const struct file_operations brd_ctl_fops = {
+ .open = nonseekable_open,
+ .unlocked_ioctl = brd_control_ioctl,
+ .owner = THIS_MODULE,
+ .llseek = noop_llseek,
+#ifdef CONFIG_COMPAT
+ .compat_ioctl = brd_control_ioctl,
+#endif
+};
+
+static struct miscdevice brd_misc = {
+ .minor = BRD_CTRL_MINOR,
+ .name = "brd-control",
+ .fops = &brd_ctl_fops,
+};
+
+MODULE_ALIAS_MISCDEV(BRD_CTRL_MINOR);
+MODULE_ALIAS("devname:brd-control");
+
static int __init brd_init(void)
{
int i, nr;
+ int err = -ENOMEM;
unsigned long range;
struct brd_device *brd, *next;
@@ -603,11 +694,18 @@ static int __init brd_init(void)
range = 1UL << MINORBITS;
}
- if (register_blkdev(RAMDISK_MAJOR, "ramdisk"))
- return -EIO;
+ err = misc_register(&brd_misc);
+ if (err < 0)
+ return err;
+
+ err = register_blkdev(RAMDISK_MAJOR, "ramdisk");
+ if (err < 0) {
+ err = -EIO;
+ goto out;
+ }
for (i = 0; i < nr; i++) {
- brd = brd_alloc(i);
+ brd = brd_alloc(i, rd_size);
if (!brd)
goto out_free;
list_add_tail(&brd->brd_list, &brd_devices);
@@ -630,8 +728,10 @@ out_free:
brd_free(brd);
}
unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
+out:
+ misc_deregister(&brd_misc);
- return -ENOMEM;
+ return err;
}
static void __exit brd_exit(void)
@@ -646,6 +746,7 @@ static void __exit brd_exit(void)
blk_unregister_region(MKDEV(RAMDISK_MAJOR, 0), range);
unregister_blkdev(RAMDISK_MAJOR, "ramdisk");
+ misc_deregister(&brd_misc);
}
module_init(brd_init);
diff --git a/include/linux/Kbuild b/include/linux/Kbuild
index fa21760..05b0d3f 100644
--- a/include/linux/Kbuild
+++ b/include/linux/Kbuild
@@ -78,6 +78,7 @@ header-y += blk_types.h
header-y += blkpg.h
header-y += blktrace_api.h
header-y += bpqether.h
+header-y += brd.h
header-y += bsg.h
header-y += can.h
header-y += capability.h
diff --git a/include/linux/brd.h b/include/linux/brd.h
new file mode 100644
index 0000000..1774b2e
--- /dev/null
+++ b/include/linux/brd.h
@@ -0,0 +1,11 @@
+#ifndef _LINUX_BRD_H__
+#define _LINUX_BRD_H__
+
+#include <linux/ioctl.h>
+
+#define BRD_CTL_MAGIC 0xF7
+
+/* /dev/brd-control ioctl commands */
+#define BRD_CTL_ADD _IOWR(BRD_CTL_MAGIC, 0, int)
+#define BRD_CTL_DEL _IOR(BRD_CTL_MAGIC, 1, int)
+#endif /* __LINUX_BRD_H__ */
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index e0deeb2..45df076 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -44,6 +44,7 @@
#define MAPPER_CTRL_MINOR 236
#define LOOP_CTRL_MINOR 237
#define VHOST_NET_MINOR 238
+#define BRD_CTRL_MINOR 239
#define MISC_DYNAMIC_MINOR 255
struct device;
--
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