[PATCH v4 2nd 2/4] pstore: support multiple pmsg instances

[Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@hitachi.com>]

From: Hiraku Toyooka <hiraku.toyooka.gu@hitachi.com>

This 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 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>
Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.kw@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>

V4:
    Rebase.
V3:
    rebase.
    merged device_create().
---
 fs/pstore/pmsg.c       | 23 ++++++++++++++++-------
 include/linux/pstore.h |  1 +
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/fs/pstore/pmsg.c b/fs/pstore/pmsg.c
index 78f6176c020f..5da5cba4b387 100644
--- a/fs/pstore/pmsg.c
+++ b/fs/pstore/pmsg.c
@@ -34,7 +34,8 @@ static ssize_t write_pmsg(struct file *file, const char __user *buf,
 		return -EFAULT;
 
 	mutex_lock(&pmsg_lock);
-	ret = psinfo->write_buf_user(PSTORE_TYPE_PMSG, 0, &id, 0, buf, 0, count,
+	ret = psinfo->write_buf_user(PSTORE_TYPE_PMSG, 0, &id,
+				     iminor(file->f_inode), buf, 0, count,
 				     psinfo);
 	mutex_unlock(&pmsg_lock);
 	return ret ? ret : count;
@@ -61,7 +62,7 @@ static char *pmsg_devnode(struct device *dev, umode_t *mode)
 
 void pstore_register_pmsg(void)
 {
-	struct device *pmsg_device;
+	int i;
 
 	pmsg_major = register_chrdev(0, PMSG_NAME, &pmsg_fops);
 	if (pmsg_major < 0) {
@@ -76,15 +77,23 @@ void pstore_register_pmsg(void)
 	}
 	pmsg_class->devnode = pmsg_devnode;
 
-	pmsg_device = device_create(pmsg_class, NULL, MKDEV(pmsg_major, 0),
-					NULL, "%s%d", PMSG_NAME, 0);
-	if (IS_ERR(pmsg_device)) {
-		pr_err("failed to create device\n");
-		goto err_device;
+	/* allocate additional /dev/pmsg[ID] */
+	for (i = 0; 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 0da29cae009b..7a5db4833b8a 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -55,6 +55,7 @@ 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,
-- 
2.11.0