kmsg: add function for adding and deleting additional buffers

Additional kmsg buffers should be created and deleted dynamically.

Adding two functions
* kmsg_sys_buffer_add() creates additional kmsg buffer returning minor
* kmsg_sys_buffer_del() deletes one based on provided minor

Change-Id: Ibb85543b830ecd186e8cf7ebdf560f72c0bba83c
Signed-off-by: Marcin Niesluchowski <m.niesluchow@samsung.com>
[Fixed bug that allow adding more buffers than available minors]
Signed-off-by: Kazimierz Krosman <k.krosman@samsung.com>

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 4147304f394b4f52cfc95e77c47709c872c2f7ef..76c404bbe5009f1e8fa8ce828aeb9a6dccf81f48 100644 (file)
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -431,6 +431,8 @@ 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);
+extern int kmsg_sys_buffer_add(size_t size, umode_t mode);
+extern void kmsg_sys_buffer_del(int minor);
 
 #else
 
@@ -449,6 +451,13 @@ static inline int kmsg_mode(int minor, umode_t *mode)
        return -ENXIO;
 }
 
+static inline int kmsg_sys_buffer_add(size_t size, umode_t mode)
+{
+       return -ENXIO;
+}
+
+static inline void kmsg_sys_buffer_del(int minor) {}
+
 #endif
 
 enum {

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2668dc729b2062cb907398996b5514e899f855e9..3d7fbacadce3186e4e9707da9de6262311f5357f 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -47,6 +47,8 @@
 #include <linux/ctype.h>
 #include <linux/uio.h>
 #include <linux/device.h>
+#include <linux/slab.h>
+#include <linux/kref.h>
 #include <linux/kdev_t.h>
 
 #include <asm/uaccess.h>
@@ -230,6 +232,7 @@ struct log_buffer {
        char *buf;              /* cyclic log buffer */
        u32 len;                /* buffer length */
        wait_queue_head_t wait; /* wait queue for kmsg buffer */
+       struct kref refcount;   /* refcount for kmsg_sys buffers */
 #endif
 /*
  * The lock protects kmsg buffer, indices, counters. This can be taken within
@@ -266,6 +269,7 @@ static u32 clear_idx;
 
 #define PREFIX_MAX             32
 #define LOG_LINE_MAX           (1024 - PREFIX_MAX)
+#define KMSG_NUM_MAX    255
 
 /* record buffer */
 #if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
@@ -282,6 +286,7 @@ static struct log_buffer log_buf = {
        .len            = __LOG_BUF_K_LEN,
        .lock           = __RAW_SPIN_LOCK_UNLOCKED(log_buf.lock),
        .wait           = __WAIT_QUEUE_HEAD_INITIALIZER(log_buf.wait),
+       .refcount       = { .refcount = { .counter = 0 } },
        .first_seq      = 0,
        .first_idx      = 0,
        .next_seq       = 0,
@@ -772,6 +777,15 @@ struct devkmsg_user {
        char buf[CONSOLE_EXT_LOG_MAX];
 };
 
+void log_buf_release(struct kref *ref)
+{
+       struct log_buffer *log_b = container_of(ref, struct log_buffer,
+                                               refcount);
+
+       kfree(log_b->buf);
+       kfree(log_b);
+}
+
 static int kmsg_sys_write(int minor, int level, const char *fmt, ...)
 {
        va_list args;
@@ -886,8 +900,21 @@ static ssize_t kmsg_read(struct log_buffer *log_b, struct file *file,
                }
 
                raw_spin_unlock_irq(&log_b->lock);
-               ret = wait_event_interruptible(log_b->wait,
-                                              user->seq != log_b->next_seq);
+
+               if (log_b == &log_buf) {
+                       ret = wait_event_interruptible(log_b->wait,
+                                               user->seq != log_b->next_seq);
+               } else {
+                       rcu_read_unlock();
+                       kref_get(&log_b->refcount);
+                       ret = wait_event_interruptible(log_b->wait,
+                                               user->seq != log_b->next_seq);
+                       if (log_b->minor == -1)
+                               ret = -ENXIO;
+                       if (kref_put(&log_b->refcount, log_buf_release))
+                               ret = -ENXIO;
+                       rcu_read_lock();
+               }
                if (ret)
                        goto out;
                raw_spin_lock_irq(&log_b->lock);
@@ -1111,8 +1138,14 @@ static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
        rcu_read_lock();
        list_for_each_entry_rcu(log_b, &log_buf.list, list) {
                if (log_b->minor == minor) {
+                       kref_get(&log_b->refcount);
+                       rcu_read_unlock();
+
                        ret = kmsg_poll(log_b, file, wait);
-                       break;
+
+                       if (kref_put(&log_b->refcount, log_buf_release))
+                               return POLLERR|POLLNVAL;
+                       return ret;
                }
        }
        rcu_read_unlock();
@@ -1228,6 +1261,88 @@ int kmsg_mode(int minor, umode_t *mode)
        return ret;
 }
 
+static DEFINE_SPINLOCK(kmsg_sys_list_lock);
+
+int kmsg_sys_buffer_add(size_t size, umode_t mode)
+{
+       unsigned long flags;
+       int minor = log_buf.minor;
+       struct log_buffer *log_b;
+       struct log_buffer *log_b_new;
+
+       if (size < LOG_LINE_MAX + PREFIX_MAX)
+               return -EINVAL;
+
+       log_b_new = kzalloc(sizeof(struct log_buffer), GFP_KERNEL);
+       if (!log_b_new)
+               return -ENOMEM;
+
+       log_b_new->buf = kmalloc(size, GFP_KERNEL);
+       if (!log_b_new->buf) {
+               kfree(log_b_new);
+               return -ENOMEM;
+       }
+
+       log_b_new->len = size;
+       log_b_new->lock = __RAW_SPIN_LOCK_UNLOCKED(log_b_new->lock);
+       init_waitqueue_head(&log_b_new->wait);
+       kref_init(&log_b_new->refcount);
+       log_b_new->mode = mode;
+
+       kref_get(&log_b_new->refcount);
+
+       spin_lock_irqsave(&kmsg_sys_list_lock, flags);
+
+       list_for_each_entry(log_b, &log_buf.list, list) {
+               if (log_b->minor - minor > 1)
+                       break;
+
+               minor = log_b->minor;
+       }
+
+       if (!(minor & MINORMASK) || (minor & MINORMASK) >= KMSG_NUM_MAX) {
+               kref_put(&log_b->refcount, log_buf_release);
+               spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+               return -ERANGE;
+       }
+
+       minor += 1;
+       log_b_new->minor = minor;
+
+       list_add_tail_rcu(&log_b_new->list, &log_b->list);
+
+       spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+
+       return minor;
+}
+
+void kmsg_sys_buffer_del(int minor)
+{
+       unsigned long flags;
+       struct log_buffer *log_b;
+
+       spin_lock_irqsave(&kmsg_sys_list_lock, flags);
+
+       list_for_each_entry(log_b, &log_buf.list, list) {
+               if (log_b->minor == minor)
+                       break;
+       }
+
+       if (log_b == &log_buf) {
+               spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+               return;
+       }
+
+       list_del_rcu(&log_b->list);
+
+       spin_unlock_irqrestore(&kmsg_sys_list_lock, flags);
+
+       log_b->minor = -1;
+       wake_up_interruptible(&log_b->wait);
+
+       kref_put(&log_b->refcount, log_buf_release);
+}
+
 #ifdef CONFIG_KEXEC
 /*
  * This appends the listed symbols to /proc/vmcore