pstore/blk: Support non-block storage devices

Add support for non-block devices (e.g. MTD). A non-block driver calls
pstore_blk_register_device() to register iself.

In addition, pstore/zone is updated to handle non-block devices,
where an erase must be done before a write. Without this, there is no
way to remove records stored to an MTD.
Signed-off-by: WeiXiong Liao <liaoweixiong@allwinnertech.com>
Link: https://lore.kernel.org/lkml/20200511233229.27745-10-keescook@chromium.org/Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

Documentation/admin-guide/pstore-blk.rst

@@ -7,8 +7,8 @@ Introduction
 ------------
 
 pstore block (pstore/blk) is an oops/panic logger that writes its logs to a
-block device before the system crashes. You can get these log files by
-mounting pstore filesystem like::
+block device and non-block device before the system crashes. You can get
+these log files by mounting pstore filesystem like::
 
     mount -t pstore pstore /sys/fs/pstore
 
@@ -24,8 +24,8 @@ Configurations for user determine how pstore/blk works, such as pmsg_size,
 kmsg_size and so on. All of them support both Kconfig and module parameters,
 but module parameters have priority over Kconfig.
 
-Configurations for driver are all about block device, such as total_size
-of block device and read/write operations.
+Configurations for driver are all about block device and non-block device,
+such as total_size of block device and read/write operations.
 
 Configurations for user
 -----------------------
@@ -152,6 +152,15 @@ driver uses ``register_pstore_blk`` to register to pstore/blk.
 .. kernel-doc:: fs/pstore/blk.c
    :identifiers: register_pstore_blk
 
+A non-block device driver uses ``register_pstore_device`` with
+``struct pstore_device_info`` to register to pstore/blk.
+
+.. kernel-doc:: fs/pstore/blk.c
+   :identifiers: register_pstore_device
+
+.. kernel-doc:: include/linux/pstore_blk.h
+   :identifiers: pstore_device_info
+
 Compression and header
 ----------------------
 

fs/pstore/blk.c

@@ -105,55 +105,22 @@ struct bdev_info {
 	_##name_;						\
 })
 
-/**
- * struct pstore_device_info - back-end pstore/blk driver structure.
- *
- * @total_size: The total size in bytes pstore/blk can use. It must be greater
- *		than 4096 and be multiple of 4096.
- * @flags:	Refer to macro starting with PSTORE_FLAGS defined in
- *		linux/pstore.h. It means what front-ends this device support.
- *		Zero means all backends for compatible.
- * @read:	The general read operation. Both of the function parameters
- *		@size and @offset are relative value to bock device (not the
- *		whole disk).
- *		On success, the number of bytes should be returned, others
- *		means error.
- * @write:	The same as @read, but the following error number:
- *		-EBUSY means try to write again later.
- *		-ENOMSG means to try next zone.
- * @panic_write:The write operation only used for panic case. It's optional
- *		if you do not care panic log. The parameters are relative
- *		value to storage.
- *		On success, the number of bytes should be returned, others
- *		excluding -ENOMSG mean error. -ENOMSG means to try next zone.
- */
-struct pstore_device_info {
-	unsigned long total_size;
-	unsigned int flags;
-	pstore_zone_read_op read;
-	pstore_zone_write_op write;
-	pstore_zone_write_op panic_write;
-};
-
-static int psblk_register_do(struct pstore_device_info *dev)
+static int __register_pstore_device(struct pstore_device_info *dev)
 {
 	int ret;
 
+	lockdep_assert_held(&pstore_blk_lock);
+
 	if (!dev || !dev->total_size || !dev->read || !dev->write)
 		return -EINVAL;
 
-	mutex_lock(&pstore_blk_lock);
-
 	/* someone already registered before */
-	if (pstore_zone_info) {
-		mutex_unlock(&pstore_blk_lock);
+	if (pstore_zone_info)
 		return -EBUSY;
-	}
+
 	pstore_zone_info = kzalloc(sizeof(struct pstore_zone_info), GFP_KERNEL);
-	if (!pstore_zone_info) {
-		mutex_unlock(&pstore_blk_lock);
+	if (!pstore_zone_info)
 		return -ENOMEM;
-	}
 
 	/* zero means not limit on which backends to attempt to store. */
 	if (!dev->flags)
@@ -179,6 +146,7 @@ static int psblk_register_do(struct pstore_device_info *dev)
 	pstore_zone_info->max_reason = max_reason;
 	pstore_zone_info->read = dev->read;
 	pstore_zone_info->write = dev->write;
+	pstore_zone_info->erase = dev->erase;
 	pstore_zone_info->panic_write = dev->panic_write;
 	pstore_zone_info->name = KBUILD_MODNAME;
 	pstore_zone_info->owner = THIS_MODULE;
@@ -188,20 +156,51 @@ static int psblk_register_do(struct pstore_device_info *dev)
 		kfree(pstore_zone_info);
 		pstore_zone_info = NULL;
 	}
+	return ret;
+}
+/**
+ * register_pstore_device() - register non-block device to pstore/blk
+ *
+ * @dev: non-block device information
+ *
+ * Return:
+ * * 0		- OK
+ * * Others	- something error.
+ */
+int register_pstore_device(struct pstore_device_info *dev)
+{
+	int ret;
+
+	mutex_lock(&pstore_blk_lock);
+	ret = __register_pstore_device(dev);
 	mutex_unlock(&pstore_blk_lock);
+
 	return ret;
 }
+EXPORT_SYMBOL_GPL(register_pstore_device);
 
-static void psblk_unregister_do(struct pstore_device_info *dev)
+static void __unregister_pstore_device(struct pstore_device_info *dev)
 {
-	mutex_lock(&pstore_blk_lock);
+	lockdep_assert_held(&pstore_blk_lock);
 	if (pstore_zone_info && pstore_zone_info->read == dev->read) {
 		unregister_pstore_zone(pstore_zone_info);
 		kfree(pstore_zone_info);
 		pstore_zone_info = NULL;
 	}
+}
+
+/**
+ * unregister_pstore_device() - unregister non-block device from pstore/blk
+ *
+ * @dev: non-block device information
+ */
+void unregister_pstore_device(struct pstore_device_info *dev)
+{
+	mutex_lock(&pstore_blk_lock);
+	__unregister_pstore_device(dev);
 	mutex_unlock(&pstore_blk_lock);
 }
+EXPORT_SYMBOL_GPL(unregister_pstore_device);
 
 /**
  * psblk_get_bdev() - open block device
@@ -396,9 +395,10 @@ static int __register_pstore_blk(struct pstore_blk_info *info)
 	dev.flags = info->flags;
 	dev.read = psblk_generic_blk_read;
 	dev.write = psblk_generic_blk_write;
+	dev.erase = NULL;
 	dev.panic_write = info->panic_write ? psblk_blk_panic_write : NULL;
 
-	ret = psblk_register_do(&dev);
+	ret = __register_pstore_device(&dev);
 	if (ret)
 		goto err_put_bdev;
 
@@ -442,7 +442,7 @@ static void __unregister_pstore_blk(unsigned int major)
 
 	lockdep_assert_held(&pstore_blk_lock);
 	if (psblk_bdev && MAJOR(psblk_bdev->bd_dev) == major) {
-		psblk_unregister_do(&dev);
+		__unregister_pstore_device(&dev);
 		psblk_put_bdev(psblk_bdev, holder);
 		blkdev_panic_write = NULL;
 		psblk_bdev = NULL;
@@ -481,6 +481,13 @@ static void __exit pstore_blk_exit(void)
 	mutex_lock(&pstore_blk_lock);
 	if (psblk_bdev)
 		__unregister_pstore_blk(MAJOR(psblk_bdev->bd_dev));
+	else {
+		struct pstore_device_info dev = { };
+
+		if (pstore_zone_info)
+			dev.read = pstore_zone_info->read;
+		__unregister_pstore_device(&dev);
+	}
 	mutex_unlock(&pstore_blk_lock);
 }
 module_exit(pstore_blk_exit);

fs/pstore/zone.c

@@ -660,15 +660,21 @@ static inline int psz_kmsg_erase(struct psz_context *cxt,
 	struct psz_buffer *buffer = zone->buffer;
 	struct psz_kmsg_header *hdr =
 		(struct psz_kmsg_header *)buffer->data;
+	size_t size;
 
 	if (unlikely(!psz_ok(zone)))
 		return 0;
+
 	/* this zone is already updated, no need to erase */
 	if (record->count != hdr->counter)
 		return 0;
 
+	size = buffer_datalen(zone) + sizeof(*zone->buffer);
 	atomic_set(&zone->buffer->datalen, 0);
-	return psz_zone_write(zone, FLUSH_META, NULL, 0, 0);
+	if (cxt->pstore_zone_info->erase)
+		return cxt->pstore_zone_info->erase(size, zone->off);
+	else
+		return psz_zone_write(zone, FLUSH_META, NULL, 0, 0);
 }
 
 static inline int psz_record_erase(struct psz_context *cxt,

include/linux/pstore_blk.h

@@ -49,6 +49,44 @@ struct pstore_blk_info {
 int  register_pstore_blk(struct pstore_blk_info *info);
 void unregister_pstore_blk(unsigned int major);
 
+/**
+ * struct pstore_device_info - back-end pstore/blk driver structure.
+ *
+ * @total_size: The total size in bytes pstore/blk can use. It must be greater
+ *		than 4096 and be multiple of 4096.
+ * @flags:	Refer to macro starting with PSTORE_FLAGS defined in
+ *		linux/pstore.h. It means what front-ends this device support.
+ *		Zero means all backends for compatible.
+ * @read:	The general read operation. Both of the function parameters
+ *		@size and @offset are relative value to bock device (not the
+ *		whole disk).
+ *		On success, the number of bytes should be returned, others
+ *		means error.
+ * @write:	The same as @read, but the following error number:
+ *		-EBUSY means try to write again later.
+ *		-ENOMSG means to try next zone.
+ * @erase:	The general erase operation for device with special removing
+ *		job. Both of the function parameters @size and @offset are
+ *		relative value to storage.
+ *		Return 0 on success and others on failure.
+ * @panic_write:The write operation only used for panic case. It's optional
+ *		if you do not care panic log. The parameters are relative
+ *		value to storage.
+ *		On success, the number of bytes should be returned, others
+ *		excluding -ENOMSG mean error. -ENOMSG means to try next zone.
+ */
+struct pstore_device_info {
+	unsigned long total_size;
+	unsigned int flags;
+	pstore_zone_read_op read;
+	pstore_zone_write_op write;
+	pstore_zone_erase_op erase;
+	pstore_zone_write_op panic_write;
+};
+
+int  register_pstore_device(struct pstore_device_info *dev);
+void unregister_pstore_device(struct pstore_device_info *dev);
+
 /**
  * struct pstore_blk_config - the pstore_blk backend configuration
  *

include/linux/pstore_zone.h

@@ -7,6 +7,7 @@
 
 typedef ssize_t (*pstore_zone_read_op)(char *, size_t, loff_t);
 typedef ssize_t (*pstore_zone_write_op)(const char *, size_t, loff_t);
+typedef ssize_t (*pstore_zone_erase_op)(size_t, loff_t);
 /**
  * struct pstore_zone_info - pstore/zone back-end driver structure
  *
@@ -27,6 +28,10 @@ typedef ssize_t (*pstore_zone_write_op)(const char *, size_t, loff_t);
  * @write:	The same as @read, but the following error number:
  *		-EBUSY means try to write again later.
  *		-ENOMSG means to try next zone.
+ * @erase:	The general erase operation for device with special removing
+ *		job. Both of the function parameters @size and @offset are
+ *		relative value to storage.
+ *		Return 0 on success and others on failure.
  * @panic_write:The write operation only used for panic case. It's optional
  *		if you do not care panic log. The parameters are relative
  *		value to storage.
@@ -45,6 +50,7 @@ struct pstore_zone_info {
 	unsigned long ftrace_size;
 	pstore_zone_read_op read;
 	pstore_zone_write_op write;
+	pstore_zone_erase_op erase;
 	pstore_zone_write_op panic_write;
 };