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Date: Thu, 15 Dec 2022 01:28:58 -0800
From: Christoph Hellwig <hch@...radead.org>
To: Sergei Shtepa <sergei.shtepa@...am.com>
Cc: axboe@...nel.dk, corbet@....net, linux-block@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/21] block, blksnap: module management interface
functions
> + ret = register_chrdev(0, THIS_MODULE->name, &ctrl_fops);
This crashed when blksnap is built into the kernel because THIS_MODULE
is NULL for that case.
But I think most of this boilerplate can be removed - just use a misc
device and use /proc/misc to find the major from userspace if anything
cares, but nothing should as the misc devices already create the
node through udev. I.e.g:
diff --git a/drivers/block/blksnap/Makefile b/drivers/block/blksnap/Makefile
index b196b17f9d9d97..cbcac12cc61d59 100644
--- a/drivers/block/blksnap/Makefile
+++ b/drivers/block/blksnap/Makefile
@@ -12,7 +12,6 @@ blksnap-y := \
main.o \
snapimage.o \
snapshot.o \
- sysfs.o \
tracker.o
obj-$(CONFIG_BLK_SNAP) += blksnap.o
diff --git a/drivers/block/blksnap/ctrl.c b/drivers/block/blksnap/ctrl.c
index 990ffb004db3f9..d1a5e3a13a19be 100644
--- a/drivers/block/blksnap/ctrl.c
+++ b/drivers/block/blksnap/ctrl.c
@@ -5,6 +5,7 @@
#include <linux/poll.h>
#include <linux/uaccess.h>
#include <linux/slab.h>
+#include <linux/miscdevice.h>
#include <uapi/linux/blksnap.h>
#include "ctrl.h"
#include "params.h"
@@ -16,16 +17,6 @@
static_assert(sizeof(uuid_t) == sizeof(struct blk_snap_uuid),
"Invalid size of struct blk_snap_uuid or uuid_t.");
-static int blk_snap_major;
-
-static long ctrl_unlocked_ioctl(struct file *filp, unsigned int cmd,
- unsigned long arg);
-
-static const struct file_operations ctrl_fops = {
- .owner = THIS_MODULE,
- .unlocked_ioctl = ctrl_unlocked_ioctl,
-};
-
static const struct blk_snap_version version = {
.major = VERSION_MAJOR,
.minor = VERSION_MINOR,
@@ -33,34 +24,6 @@ static const struct blk_snap_version version = {
.build = VERSION_BUILD,
};
-int get_blk_snap_major(void)
-{
- return blk_snap_major;
-}
-
-int ctrl_init(void)
-{
- int ret;
-
- ret = register_chrdev(0, THIS_MODULE->name, &ctrl_fops);
- if (ret < 0) {
- pr_err("Failed to register a character device. errno=%d\n",
- abs(blk_snap_major));
- return ret;
- }
-
- blk_snap_major = ret;
- pr_info("Register control device [%d:0].\n", blk_snap_major);
- return 0;
-}
-
-void ctrl_done(void)
-{
- pr_info("Unregister control device\n");
-
- unregister_chrdev(blk_snap_major, THIS_MODULE->name);
-}
-
static int ioctl_version(unsigned long arg)
{
if (copy_to_user((void *)arg, &version, sizeof(version))) {
@@ -408,3 +371,24 @@ static long ctrl_unlocked_ioctl(struct file *filp, unsigned int cmd,
return blk_snap_ioctl_table[nr](arg);
}
+
+static const struct file_operations blksnap_ctrl_fops = {
+ .owner = THIS_MODULE,
+ .unlocked_ioctl = ctrl_unlocked_ioctl,
+};
+
+static struct miscdevice blksnap_ctrl_misc = {
+ .minor = MISC_DYNAMIC_MINOR,
+ .name = "blksnap-control",
+ .fops = &blksnap_ctrl_fops,
+};
+
+int ctrl_init(void)
+{
+ return misc_register(&blksnap_ctrl_misc);
+}
+
+void ctrl_done(void)
+{
+ misc_deregister(&blksnap_ctrl_misc);
+}
diff --git a/drivers/block/blksnap/ctrl.h b/drivers/block/blksnap/ctrl.h
index ade3f1cf57e90c..88f4b05296e575 100644
--- a/drivers/block/blksnap/ctrl.h
+++ b/drivers/block/blksnap/ctrl.h
@@ -2,8 +2,6 @@
#ifndef __BLK_SNAP_CTRL_H
#define __BLK_SNAP_CTRL_H
-int get_blk_snap_major(void);
-
int ctrl_init(void);
void ctrl_done(void);
#endif /* __BLK_SNAP_CTRL_H */
diff --git a/drivers/block/blksnap/main.c b/drivers/block/blksnap/main.c
index a7939efc6497b9..f8b6f5c406ed7c 100644
--- a/drivers/block/blksnap/main.c
+++ b/drivers/block/blksnap/main.c
@@ -6,7 +6,6 @@
#include "version.h"
#include "params.h"
#include "ctrl.h"
-#include "sysfs.h"
#include "snapimage.h"
#include "snapshot.h"
#include "tracker.h"
@@ -44,8 +43,6 @@ static int __init blk_snap_init(void)
result = ctrl_init();
if (result)
return result;
-
- result = sysfs_initialize();
return result;
}
@@ -53,7 +50,6 @@ static void __exit blk_snap_exit(void)
{
pr_info("Unloading module\n");
- sysfs_finalize();
ctrl_done();
diff_io_done();
diff --git a/drivers/block/blksnap/sysfs.c b/drivers/block/blksnap/sysfs.c
deleted file mode 100644
index 6f53c4217d6c7b..00000000000000
--- a/drivers/block/blksnap/sysfs.c
+++ /dev/null
@@ -1,80 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#define pr_fmt(fmt) KBUILD_MODNAME "-sysfs: " fmt
-
-#include <linux/module.h>
-#include <linux/blkdev.h>
-#include <linux/sysfs.h>
-#include <linux/device.h>
-#include <uapi/linux/blksnap.h>
-#include "sysfs.h"
-#include "ctrl.h"
-
-static ssize_t major_show(struct class *class, struct class_attribute *attr,
- char *buf)
-{
- sprintf(buf, "%d", get_blk_snap_major());
- return strlen(buf);
-}
-
-/* Declare class_attr_major */
-CLASS_ATTR_RO(major);
-
-static struct class *blk_snap_class;
-
-static struct device *blk_snap_device;
-
-int sysfs_initialize(void)
-{
- struct device *dev;
- int res;
-
- blk_snap_class = class_create(THIS_MODULE, THIS_MODULE->name);
- if (IS_ERR(blk_snap_class)) {
- res = PTR_ERR(blk_snap_class);
-
- pr_err("Bad class create. errno=%d\n", abs(res));
- return res;
- }
-
- pr_info("Create 'major' sysfs attribute\n");
- res = class_create_file(blk_snap_class, &class_attr_major);
- if (res) {
- pr_err("Failed to create 'major' sysfs file\n");
-
- class_destroy(blk_snap_class);
- blk_snap_class = NULL;
- return res;
- }
-
- dev = device_create(blk_snap_class, NULL,
- MKDEV(get_blk_snap_major(), 0), NULL,
- THIS_MODULE->name);
- if (IS_ERR(dev)) {
- res = PTR_ERR(dev);
- pr_err("Failed to create device, errno=%d\n", abs(res));
-
- class_remove_file(blk_snap_class, &class_attr_major);
- class_destroy(blk_snap_class);
- blk_snap_class = NULL;
- return res;
- }
-
- blk_snap_device = dev;
- return res;
-}
-
-void sysfs_finalize(void)
-{
- pr_info("Cleanup sysfs\n");
-
- if (blk_snap_device) {
- device_unregister(blk_snap_device);
- blk_snap_device = NULL;
- }
-
- if (blk_snap_class != NULL) {
- class_remove_file(blk_snap_class, &class_attr_major);
- class_destroy(blk_snap_class);
- blk_snap_class = NULL;
- }
-}
diff --git a/drivers/block/blksnap/sysfs.h b/drivers/block/blksnap/sysfs.h
deleted file mode 100644
index 5fc200d3678964..00000000000000
--- a/drivers/block/blksnap/sysfs.h
+++ /dev/null
@@ -1,7 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef __BLK_SNAP_SYSFS_H
-#define __BLK_SNAP_SYSFS_H
-
-int sysfs_initialize(void);
-void sysfs_finalize(void);
-#endif /* __BLK_SNAP_SYSFS_H */
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