[RFC v2 4/9] kmsg: add additional buffers support to memory class

[Paul Osmialowski]

From: Marcin Niesluchowski <m.niesluchow@xxxxxxxxxxx>

Memory class does not support additional kmsg buffers.

Add additional kmsg buffers support to:
* devnode() callback of "mem" class
* file operations of major "mem" character device

Signed-off-by: Marcin Niesluchowski <m.niesluchow@xxxxxxxxxxx>
---
 drivers/char/mem.c     | 27 ++++++++++++++++++++-------
 include/linux/printk.h | 32 ++++++++++++++++++++++++++++++++
 kernel/printk/printk.c | 43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 95 insertions(+), 7 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 6b1721f..7d46234 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -799,9 +799,6 @@ static const struct memdev {
 	 [7] = { "full", 0666, &full_fops, 0 },
 	 [8] = { "random", 0666, &random_fops, 0 },
 	 [9] = { "urandom", 0666, &urandom_fops, 0 },
-#ifdef CONFIG_PRINTK
-	[11] = { "kmsg", 0644, &kmsg_fops, 0 },
-#endif
 };
 
 static int memory_open(struct inode *inode, struct file *filp)
@@ -811,7 +808,7 @@ static int memory_open(struct inode *inode, struct file *filp)
 
 	minor = iminor(inode);
 	if (minor >= ARRAY_SIZE(devlist))
-		return -ENXIO;
+		return kmsg_memory_open(inode, filp);
 
 	dev = &devlist[minor];
 	if (!dev->fops)
@@ -833,16 +830,28 @@ static const struct file_operations memory_fops = {
 
 static char *mem_devnode(struct device *dev, umode_t *mode)
 {
-	if (mode && devlist[MINOR(dev->devt)].mode)
-		*mode = devlist[MINOR(dev->devt)].mode;
+	int minor = MINOR(dev->devt);
+
+	if (!mode)
+		goto out;
+
+	if (minor >= ARRAY_SIZE(devlist)) {
+		kmsg_mode(minor, mode);
+		goto out;
+	}
+
+	if (devlist[minor].mode)
+		*mode = devlist[minor].mode;
+out:
 	return NULL;
 }
 
-static struct class *mem_class;
+struct class *mem_class;
 
 static int __init chr_dev_init(void)
 {
 	int minor;
+	struct device *kmsg;
 
 	if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
 		printk("unable to get major %d for memory devs\n", MEM_MAJOR);
@@ -866,6 +875,10 @@ static int __init chr_dev_init(void)
 			      NULL, devlist[minor].name);
 	}
 
+	kmsg = init_kmsg(KMSG_MINOR, 0644);
+	if (IS_ERR(kmsg))
+		return PTR_ERR(kmsg);
+
 	return tty_init();
 }
 
diff --git a/include/linux/printk.h b/include/linux/printk.h
index 9729565..67840e0 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -417,8 +417,40 @@ do {									\
 	no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
 #endif
 
+struct file;
+struct inode;
+
+#ifdef CONFIG_PRINTK
+
+extern struct class *mem_class;
+
+#define KMSG_MINOR	11
+
 extern const struct file_operations kmsg_fops;
 
+extern struct device *init_kmsg(int minor, umode_t mode);
+extern int kmsg_memory_open(struct inode *inode, struct file *filp);
+extern int kmsg_mode(int minor, umode_t *mode);
+
+#else
+
+static inline struct device *init_kmsg(int minor, umode_t mode)
+{
+	return NULL;
+}
+
+static inline int kmsg_memory_open(struct inode *inode, struct file *filp)
+{
+	return -ENXIO;
+}
+
+static inline int kmsg_mode(int minor, umode_t *mode)
+{
+	return -ENXIO;
+}
+
+#endif
+
 enum {
 	DUMP_PREFIX_NONE,
 	DUMP_PREFIX_ADDRESS,
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 0d4d726..3157239 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -46,6 +46,8 @@
 #include <linux/utsname.h>
 #include <linux/ctype.h>
 #include <linux/uio.h>
+#include <linux/device.h>
+#include <linux/kdev_t.h>
 
 #include <asm/uaccess.h>
 
@@ -253,6 +255,7 @@ struct log_buffer {
 	u64 next_seq;
 #ifdef CONFIG_PRINTK
 	u32 next_idx;		/* index of the next record to store */
+	int mode;		/* mode of device */
 	int minor;		/* minor representing buffer device */
 #endif
 };
@@ -295,6 +298,7 @@ static struct log_buffer log_buf = {
 	.first_idx	= 0,
 	.next_seq	= 0,
 	.next_idx	= 0,
+	.mode		= 0,
 	.minor		= 0,
 };
 
@@ -1216,6 +1220,45 @@ const struct file_operations kmsg_fops = {
 	.release = devkmsg_release,
 };
 
+/* Should be used for device registration */
+struct device *init_kmsg(int minor, umode_t mode)
+{
+	log_buf.minor = minor;
+	log_buf.mode = mode;
+	return device_create(mem_class, NULL, MKDEV(MEM_MAJOR, minor),
+			NULL, "kmsg");
+}
+
+int kmsg_memory_open(struct inode *inode, struct file *filp)
+{
+	filp->f_op = &kmsg_fops;
+
+	return kmsg_fops.open(inode, filp);
+}
+
+int kmsg_mode(int minor, umode_t *mode)
+{
+	int ret = -ENXIO;
+	struct log_buffer *log_b;
+
+	if (minor == log_buf.minor) {
+		*mode = log_buf.mode;
+		return 0;
+	}
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(log_b, &log_buf.list, list) {
+		if (log_b->minor == minor) {
+			*mode = log_b->mode;
+			ret = 0;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+
 #ifdef CONFIG_KEXEC_CORE
 /*
  * This appends the listed symbols to /proc/vmcore
-- 
1.9.1

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