pstore: use mount option instead sysfs to tweak kmsg_bytes

/sys/fs is a somewhat strange way to tweak what could more
obviously be tuned with a mount option.

Suggested-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/ABI/testing/pstore

···
 Where:		/dev/pstore/...
-Date:		January 2011
-Kernel Version: 2.6.38
+Date:		March 2011
+Kernel Version: 2.6.39
 Contact:	[e-mail]
 Description:	Generic interface to platform dependent persistent storage.
 
···
 		of the console log is captured, but other interesting
 		data can also be saved.
 
-		# mount -t pstore - /dev/pstore
+		# mount -t pstore -o kmsg_bytes=8000 - /dev/pstore
 
 		$ ls -l /dev/pstore
 		total 0
···
 		will be saved elsewhere and erased from persistent store
 		soon after boot to free up space ready for the next
 		catastrophe.
+
+		The 'kmsg_bytes' mount option changes the target amount of
+		data saved on each oops/panic. Pstore saves (possibly
+		multiple) files based on the record size of the underlying
+		persistent storage until at least this amount is reached.
+		Default is 10 Kbytes.

Documentation/ABI/testing/sysfs-fs-pstore

···
-What:		/sys/fs/pstore/kmsg_bytes
-Date:		January 2011
-Kernel Version: 2.6.38
-Contact:	"Tony Luck" <[e-mail]>
-Description:
-		Controls amount of console log that will be saved
-		to persistent store on oops/panic.

fs/pstore/inode.c

···
 #include <linux/string.h>
 #include <linux/mount.h>
 #include <linux/ramfs.h>
+#include <linux/parser.h>
 #include <linux/sched.h>
 #include <linux/magic.h>
 #include <linux/pstore.h>
···
 	return inode;
 }
 
+enum {
+	Opt_kmsg_bytes, Opt_err
+};
+
+static const match_table_t tokens = {
+	{Opt_kmsg_bytes, "kmsg_bytes=%u"},
+	{Opt_err, NULL}
+};
+
+static void parse_options(char *options)
+{
+	char		*p;
+	substring_t	args[MAX_OPT_ARGS];
+	int		option;
+
+	if (!options)
+		return;
+
+	while ((p = strsep(&options, ",")) != NULL) {
+		int token;
+
+		if (!*p)
+			continue;
+
+		token = match_token(p, tokens, args);
+		switch (token) {
+		case Opt_kmsg_bytes:
+			if (!match_int(&args[0], &option))
+				pstore_set_kmsg_bytes(option);
+			break;
+		}
+	}
+}
+
+static int pstore_remount(struct super_block *sb, int *flags, char *data)
+{
+	parse_options(data);
+
+	return 0;
+}
+
 static const struct super_operations pstore_ops = {
 	.statfs		= simple_statfs,
 	.drop_inode	= generic_delete_inode,
 	.evict_inode	= pstore_evict_inode,
+	.remount_fs	= pstore_remount,
 	.show_options	= generic_show_options,
 };
 
···
 	sb->s_op		= &pstore_ops;
 	sb->s_time_gran		= 1;
 
+	parse_options(data);
+
 	inode = pstore_get_inode(sb, NULL, S_IFDIR | 0755, 0);
 	if (!inode) {
 		err = -ENOMEM;
···
 
 static int __init init_pstore_fs(void)
 {
-	int rc = 0;
-	struct kobject *pstorefs_kobj;
-
-	pstorefs_kobj = kobject_create_and_add("pstore", fs_kobj);
-	if (!pstorefs_kobj) {
-		rc = -ENOMEM;
-		goto done;
-	}
-
-	rc = sysfs_create_file(pstorefs_kobj, &pstore_kmsg_bytes_attr.attr);
-	if (rc)
-		goto done1;
-
-	rc = register_filesystem(&pstore_fs_type);
-	if (rc == 0)
-		goto done;
-
-	sysfs_remove_file(pstorefs_kobj, &pstore_kmsg_bytes_attr.attr);
-done1:
-	kobject_put(pstorefs_kobj);
-done:
-	return rc;
+	return register_filesystem(&pstore_fs_type);
 }
 module_init(init_pstore_fs)
 

fs/pstore/internal.h

···
+extern void	pstore_set_kmsg_bytes(int);
 extern void	pstore_get_records(void);
 extern int	pstore_mkfile(enum pstore_type_id, char *psname, u64 id,
 			      char *data, size_t size,
 			      struct timespec time, int (*erase)(u64));
 extern int	pstore_is_mounted(void);
-
-extern struct kobj_attribute pstore_kmsg_bytes_attr;

fs/pstore/platform.c

···
 static DEFINE_SPINLOCK(pstore_lock);
 static struct pstore_info *psinfo;
 
-/* How much of the console log to snapshot. /sys/fs/pstore/kmsg_bytes */
+/* How much of the console log to snapshot */
 static unsigned long kmsg_bytes = 10240;
 
-static ssize_t b_show(struct kobject *kobj,
-		      struct kobj_attribute *attr, char *buf)
+void pstore_set_kmsg_bytes(int bytes)
 {
-	return snprintf(buf, PAGE_SIZE, "%lu\n", kmsg_bytes);
+	kmsg_bytes = bytes;
 }
-
-static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
-		       const char *buf, size_t count)
-{
-	return (sscanf(buf, "%lu", &kmsg_bytes) > 0) ? count : 0;
-}
-
-struct kobj_attribute pstore_kmsg_bytes_attr =
-	__ATTR(kmsg_bytes, S_IRUGO | S_IWUSR, b_show, b_store);
 
 /* Tag each group of saved records with a sequence number */
 static int	oopscount;