[PATCH v6 5/8] kmsg: add function for adding and deleting additional buffers

Kazimierz Krosman
2016-02-24T11:53:44Z

From: Marcin Niesluchowski <m.niesluchow@samsung.com>

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

Signed-off-by: Marcin Niesluchowski <m.niesluchow@samsung.com>
Signed-off-by: Paul Osmialowski <p.osmialowsk@samsung.com>
[Rebased kmsg patch v5 on Linux 4.5-rc5]
Signed-off-by: Kazimierz Krosman <k.krosman@samsung.com>
---
include/linux/printk.h | 9 +++++
kernel/printk/kmsg.c | 107 +++++++++++++++++++++++++++++++++++++++++++++++--
kernel/printk/printk.c | 12 ++++++
kernel/printk/printk.h | 4 ++
4 files changed, 129 insertions(+), 3 deletions(-)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 342e9d0..c146ee4 100644
--- 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/kmsg.c b/kernel/printk/kmsg.c
index b5e07ff..82bc282 100644
--- a/kernel/printk/kmsg.c
+++ b/kernel/printk/kmsg.c
@@ -19,6 +19,7 @@
#include <linux/device.h>
#include <linux/major.h>
#include <linux/kdev_t.h>
+#include <linux/kref.h>

#include <asm/uaccess.h>

@@ -141,8 +142,20 @@ 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);
@@ -311,8 +324,14 @@ 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();
@@ -428,6 +447,88 @@ 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)) {
+ 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);
+}
+
static DEFINE_SPINLOCK(dump_list_lock);
static LIST_HEAD(dump_list);

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index d8626ee..fd5991d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -42,6 +42,8 @@
#include <linux/irq_work.h>
#include <linux/utsname.h>
#include <linux/ctype.h>
+#include <linux/kref.h>
+#include <linux/slab.h>

#include <asm/uaccess.h>
#include <asm-generic/sections.h>
@@ -171,6 +173,7 @@ 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,
@@ -216,6 +219,15 @@ u32 log_buf_len_get(void)
return log_buf.len;
}

+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);
+}
+
/*
* Check whether there is enough free space for the given message.
*
diff --git a/kernel/printk/printk.h b/kernel/printk/printk.h
index e5c8a46..a873c27 100644
--- a/kernel/printk/printk.h
+++ b/kernel/printk/printk.h
@@ -5,6 +5,7 @@
#include <linux/spinlock_types.h>
#include <linux/types.h>
#include <linux/wait.h>
+#include <linux/kref.h>

#ifdef CONFIG_PRINTK

@@ -111,6 +112,7 @@ 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
@@ -139,6 +141,8 @@ struct log_buffer {

extern struct log_buffer log_buf;

+void log_buf_release(struct kref *ref);
+
ssize_t msg_print_ext_header(char *buf, size_t size,
struct printk_log *msg, u64 seq,
enum log_flags prev_flags);
--
1.9.1