[printk,v4,7/8,v2] printk: use printk_buffers for devkmsg
Commit Message
Replace the buffers in struct devkmsg_user with a struct
printk_buffers. This reduces the number of buffers to track.
As a side-effect, @text_buf was 8kB large, even though it only
needed to be the max size of a ringbuffer record. By switching to
struct printk_buffers, ~7kB less memory is allocated when opening
/dev/kmsg.
And since struct printk_buffers will be used now, reduce duplicate
code by calling printk_get_next_message() to handle the record
reading and formatting.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
kernel/printk/printk.c | 40 ++++++++++++++++------------------------
1 file changed, 16 insertions(+), 24 deletions(-)
Comments
On Thu 2023-01-05 13:22:16, John Ogness wrote:
> Replace the buffers in struct devkmsg_user with a struct
> printk_buffers. This reduces the number of buffers to track.
>
> As a side-effect, @text_buf was 8kB large, even though it only
> needed to be the max size of a ringbuffer record. By switching to
> struct printk_buffers, ~7kB less memory is allocated when opening
> /dev/kmsg.
>
> And since struct printk_buffers will be used now, reduce duplicate
> code by calling printk_get_next_message() to handle the record
> reading and formatting.
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
> ---
> kernel/printk/printk.c | 40 ++++++++++++++++------------------------
> 1 file changed, 16 insertions(+), 24 deletions(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 4fb7d29fb05d..32996b0c5d03 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -695,16 +695,14 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
> return len;
> }
>
> +static bool printk_get_next_message(struct printk_message *pmsg, u64 seq, bool is_extended);
> +
> /* /dev/kmsg - userspace message inject/listen interface */
> struct devkmsg_user {
> atomic64_t seq;
> struct ratelimit_state rs;
> struct mutex lock;
> - char buf[CONSOLE_EXT_LOG_MAX];
> -
> - struct printk_info info;
> - char text_buf[CONSOLE_EXT_LOG_MAX];
> - struct printk_record record;
> + struct printk_buffers pbufs;
> };
>
> static __printf(3, 4) __cold
> @@ -786,8 +784,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> {
> struct devkmsg_user *user = file->private_data;
> - struct printk_record *r = &user->record;
> - size_t len;
> + char *outbuf = &user->pbufs.outbuf[0];
> + struct printk_message pmsg = {
> + .pbufs = &user->pbufs,
> + };
> ssize_t ret;
>
> if (!user)
> @@ -797,7 +797,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
> if (ret)
> return ret;
>
> - if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
> + while (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true)) {
A problem is that printk_get_next_message() does not format the
message when it shoud get supressed on the console.
I would solve it be adding a parameter to printk_get_next_message() that
will tell whether to suppress or not, e.g. @can_suppress.
> if (file->f_flags & O_NONBLOCK) {
> ret = -EAGAIN;
> goto out;
> @@ -814,36 +814,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
> * This pairs with __wake_up_klogd:A.
> */
> ret = wait_event_interruptible(log_wait,
> - prb_read_valid(prb,
> - atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
> + prb_read_valid(prb, atomic64_read(&user->seq),
> + NULL)); /* LMM(devkmsg_read:A) */
The above change from "if" to "while" could be avoided if we use
printk_get_next_message() here as well. It looks slightly more
strightfoward to me. Or do I miss something, please?
> if (ret)
> goto out;
> }
>
Otherwise, I like this change. It simplifies the code.
Best Regards,
Petr
On 2023-01-06, Petr Mladek <pmladek@suse.com> wrote:
>> - if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
>> + while (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true)) {
>
> A problem is that printk_get_next_message() does not format the
> message when it shoud get supressed on the console.
Nice catch. I missed that.
> I would solve it be adding a parameter to printk_get_next_message()
> that will tell whether to suppress or not, e.g. @can_suppress.
OK.
>> if (file->f_flags & O_NONBLOCK) {
>> ret = -EAGAIN;
>> goto out;
>> @@ -814,36 +814,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
>> * This pairs with __wake_up_klogd:A.
>> */
>> ret = wait_event_interruptible(log_wait,
>> - prb_read_valid(prb,
>> - atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
>> + prb_read_valid(prb, atomic64_read(&user->seq),
>> + NULL)); /* LMM(devkmsg_read:A) */
>
> The above change from "if" to "while" could be avoided if we use
> printk_get_next_message() here as well. It looks slightly more
> strightfoward to me.
Yes, that is better. A loop is overkill here.
John
@@ -695,16 +695,14 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
return len;
}
+static bool printk_get_next_message(struct printk_message *pmsg, u64 seq, bool is_extended);
+
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
atomic64_t seq;
struct ratelimit_state rs;
struct mutex lock;
- char buf[CONSOLE_EXT_LOG_MAX];
-
- struct printk_info info;
- char text_buf[CONSOLE_EXT_LOG_MAX];
- struct printk_record record;
+ struct printk_buffers pbufs;
};
static __printf(3, 4) __cold
@@ -786,8 +784,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
struct devkmsg_user *user = file->private_data;
- struct printk_record *r = &user->record;
- size_t len;
+ char *outbuf = &user->pbufs.outbuf[0];
+ struct printk_message pmsg = {
+ .pbufs = &user->pbufs,
+ };
ssize_t ret;
if (!user)
@@ -797,7 +797,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
if (ret)
return ret;
- if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {
+ while (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true)) {
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
goto out;
@@ -814,36 +814,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
* This pairs with __wake_up_klogd:A.
*/
ret = wait_event_interruptible(log_wait,
- prb_read_valid(prb,
- atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */
+ prb_read_valid(prb, atomic64_read(&user->seq),
+ NULL)); /* LMM(devkmsg_read:A) */
if (ret)
goto out;
}
- if (r->info->seq != atomic64_read(&user->seq)) {
+ if (pmsg.dropped) {
/* our last seen message is gone, return error and reset */
- atomic64_set(&user->seq, r->info->seq);
+ atomic64_set(&user->seq, pmsg.seq);
ret = -EPIPE;
goto out;
}
- len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);
- len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,
- &r->text_buf[0], r->info->text_len,
- &r->info->dev_info);
+ atomic64_set(&user->seq, pmsg.seq + 1);
- atomic64_set(&user->seq, r->info->seq + 1);
-
- if (len > count) {
+ if (pmsg.outbuf_len > count) {
ret = -EINVAL;
goto out;
}
- if (copy_to_user(buf, user->buf, len)) {
+ if (copy_to_user(buf, outbuf, pmsg.outbuf_len)) {
ret = -EFAULT;
goto out;
}
- ret = len;
+ ret = pmsg.outbuf_len;
out:
mutex_unlock(&user->lock);
return ret;
@@ -937,9 +932,6 @@ static int devkmsg_open(struct inode *inode, struct file *file)
mutex_init(&user->lock);
- prb_rec_init_rd(&user->record, &user->info,
- &user->text_buf[0], sizeof(user->text_buf));
-
atomic64_set(&user->seq, prb_first_valid_seq(prb));
file->private_data = user;