block2mtd.c: Make kernel boot command line arguments work (try 4)

Trying to pass kernel command line arguments to block2mtd at boot-time does
not work currently. block2mtd_setup() is called so early that kmalloc()
fails nevermind being able to do open_bdev_excl() (which requires rootfs to
be mounted. This patch only saves the option string at the early boot stage,
and parses them later when block2mtd_init() is called. If open_bdev_excl()
fails, open_by_devnum(name_to_dev_t()) is tried instead, which makes it
possible to initialize the driver before rootfs has been mounted. Also gets
rid of the superfluous parse_name() that only checks if name is longer than
80 chars and copies it to a string that is not kfreed.

With this patch, I can boot statically compiled block2mtd, and mount jffs2
as rootfs (without modules or initrd), with lilo config like this:

   root=/dev/mtdblock0
   append="rootfstype=jffs2 block2mtd.block2mtd=/dev/hdc2,65536"

(Note that rootfstype=jffs2 is required, since the kernel only tries
filesystems without "nodev" attribute by default, and jffs is "nodev").

Compared to first version of this patch, this one does not copy the
parameters to the global buffer if init has already been called, and the
global array is marked as __initdata.

Compared to the second version of this patch, module build is fixed.

Compared to the third version of this patch, statically compiled block2mtd
driver with no boot-time parameter no longer gives spurious error 'cannot
open device ""'
Signed-off-by: Ville Herva <vherva@vianova.fi>
Acked-by: Jörn Engel <joern@wohnheim.fh-wedel.de>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/devices/block2mtd.c

@@ -18,6 +18,7 @@
 #include <linux/mtd/mtd.h>
 #include <linux/buffer_head.h>
 #include <linux/mutex.h>
+#include <linux/mount.h>
 
 #define VERSION "$Revision: 1.30 $"
 
@@ -236,6 +237,8 @@ static int _block2mtd_write(struct block2mtd_dev *dev, const u_char *buf,
 	}
 	return 0;
 }
+
+
 static int block2mtd_write(struct mtd_info *mtd, loff_t to, size_t len,
 		size_t *retlen, const u_char *buf)
 {
@@ -299,6 +302,19 @@ static struct block2mtd_dev *add_device(char *devname, int erase_size)
 
 	/* Get a handle on the device */
 	bdev = open_bdev_excl(devname, O_RDWR, NULL);
+#ifndef MODULE
+	if (IS_ERR(bdev)) {
+
+		/* We might not have rootfs mounted at this point. Try
+		   to resolve the device name by other means. */
+
+		dev_t dev = name_to_dev_t(devname);
+		if (dev != 0) {
+			bdev = open_by_devnum(dev, FMODE_WRITE | FMODE_READ);
+		}
+	}
+#endif
+
 	if (IS_ERR(bdev)) {
 		ERROR("error: cannot open device %s", devname);
 		goto devinit_err;
@@ -393,26 +409,6 @@ static int parse_num(size_t *num, const char *token)
 }
 
 
-static int parse_name(char **pname, const char *token, size_t limit)
-{
-	size_t len;
-	char *name;
-
-	len = strlen(token) + 1;
-	if (len > limit)
-		return -ENOSPC;
-
-	name = kmalloc(len, GFP_KERNEL);
-	if (!name)
-		return -ENOMEM;
-
-	strcpy(name, token);
-
-	*pname = name;
-	return 0;
-}
-
-
 static inline void kill_final_newline(char *str)
 {
 	char *newline = strrchr(str, '\n');
@@ -426,9 +422,15 @@ static inline void kill_final_newline(char *str)
 	return 0;				\
 } while (0)
 
-static int block2mtd_setup(const char *val, struct kernel_param *kp)
+#ifndef MODULE
+static int block2mtd_init_called = 0;
+static __initdata char block2mtd_paramline[80 + 12]; /* 80 for device, 12 for erase size */
+#endif
+
+
+static int block2mtd_setup2(const char *val)
 {
-	char buf[80+12]; /* 80 for device, 12 for erase size */
+	char buf[80 + 12]; /* 80 for device, 12 for erase size */
 	char *str = buf;
 	char *token[2];
 	char *name;
@@ -450,13 +452,9 @@ static int block2mtd_setup(const char *val, struct kernel_param *kp)
 	if (!token[0])
 		parse_err("no argument");
 
-	ret = parse_name(&name, token[0], 80);
-	if (ret == -ENOMEM)
-		parse_err("out of memory");
-	if (ret == -ENOSPC)
-		parse_err("name too long");
-	if (ret)
-		return 0;
+	name = token[0];
+	if (strlen(name) + 1 > 80)
+		parse_err("device name too long");
 
 	if (token[1]) {
 		ret = parse_num(&erase_size, token[1]);
@@ -472,13 +470,48 @@ static int block2mtd_setup(const char *val, struct kernel_param *kp)
 }
 
 
+static int block2mtd_setup(const char *val, struct kernel_param *kp)
+{
+#ifdef MODULE
+	return block2mtd_setup2(val);
+#else
+	/* If more parameters are later passed in via
+	   /sys/module/block2mtd/parameters/block2mtd
+	   and block2mtd_init() has already been called,
+	   we can parse the argument now. */
+
+	if (block2mtd_init_called)
+		return block2mtd_setup2(val);
+
+	/* During early boot stage, we only save the parameters
+	   here. We must parse them later: if the param passed
+	   from kernel boot command line, block2mtd_setup() is
+	   called so early that it is not possible to resolve
+	   the device (even kmalloc() fails). Deter that work to
+	   block2mtd_setup2(). */
+
+	strlcpy(block2mtd_paramline, val, sizeof(block2mtd_paramline));
+
+	return 0;
+#endif
+}
+
+
 module_param_call(block2mtd, block2mtd_setup, NULL, NULL, 0200);
 MODULE_PARM_DESC(block2mtd, "Device to use. \"block2mtd=<dev>[,<erasesize>]\"");
 
 static int __init block2mtd_init(void)
 {
+	int ret = 0;
 	INFO("version " VERSION);
-	return 0;
+
+#ifndef MODULE
+	if (strlen(block2mtd_paramline))
+		ret = block2mtd_setup2(block2mtd_paramline);
+	block2mtd_init_called = 1;
+#endif
+
+	return ret;
 }