[PATCH 3/5] pstore: support multiple pmsg instances

[Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>]

This patch enables pmsg to deal with multiple instances. One possible
use is content priority control on limited persistent store space. By
using different buffers, we can prevent important messages from being
overwritten by less important messages.

When a pstore backend module specifies the number of instances (num_pmsg)
in pstore_info, multiple /dev/pmsg[ID] appear. (ID is an integer
starting at 0. It corresponds to minor number of the each char device.)
Writes to each /dev/pmsg[ID] are isolated each other. After reboot, the
contents are available in /sys/fs/pstore/pmsg-[backend]-[ID].

Signed-off-by: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>
Cc: Anton Vorontsov <anton@enomsg.org>
Cc: Colin Cross <ccross@android.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mark Salyzyn <salyzyn@android.com>
Cc: Seiji Aguchi <seiji.aguchi.tr@hitachi.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-kernel@vger.kernel.org
---
 fs/pstore/pmsg.c       |   20 ++++++++++++++++++--
 include/linux/pstore.h |    1 +
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c
index feb5dd2..3467d63 100644
--- a/fs/pstore/pmsg.c
+++ b/fs/pstore/pmsg.c
@@ -50,8 +50,8 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf,
 			vfree(buffer);
 			return -EFAULT;
 		}
-		psinfo->write_buf(PSTORE_TYPE_PMSG, 0, &id, 0, buffer, 0, c,
-				  psinfo);
+		psinfo->write_buf(PSTORE_TYPE_PMSG, 0, &id,
+				  iminor(file->f_inode), buffer, 0, c, psinfo);
 
 		i += c;
 	}
@@ -83,6 +83,7 @@ static char *pmsg_devnode(struct device *dev, umode_t *mode)
 void pstore_register_pmsg(void)
 {
 	struct device *pmsg_device;
+	int i = 0;
 
 	pmsg_major = register_chrdev(0, PMSG_NAME, &pmsg_fops);
 	if (pmsg_major < 0) {
@@ -103,9 +104,24 @@ void pstore_register_pmsg(void)
 		pr_err("failed to create device\n");
 		goto err_device;
 	}
+
+	/* allocate additional /dev/pmsg[ID] */
+	for (i = 1; i < psinfo->num_pmsg; i++) {
+		struct device *pmsg_device;
+
+		pmsg_device = device_create(pmsg_class, NULL,
+					    MKDEV(pmsg_major, i), NULL, "%s%d",
+					    PMSG_NAME, i);
+		if (IS_ERR(pmsg_device)) {
+			pr_err("failed to create device\n");
+			goto err_device;
+		}
+	}
 	return;
 
 err_device:
+	for (i--; i >= 0; i--)
+		device_destroy(pmsg_class, MKDEV(pmsg_major, i));
 	class_destroy(pmsg_class);
 err_class:
 	unregister_chrdev(pmsg_major, PMSG_NAME);
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index 8e7a25b..7cffc9d 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -54,6 +54,7 @@ struct pstore_info {
 	size_t		bufsize;
 	struct mutex	read_mutex;	/* serialize open/read/close */
 	int		flags;
+	unsigned int	num_pmsg;
 	int		(*open)(struct pstore_info *psi);
 	int		(*close)(struct pstore_info *psi);
 	ssize_t		(*read)(u64 *id, enum pstore_type_id *type,