printk: convert byte-buffer to variable-length record buffer (7ff9554b) · Commits · 戴 / test

- Record-based stream instead of the traditional byte stream buffer. All records carry a 64 bit timestamp, the syslog facility and priority in the record header. - Records consume almost the same amount, sometimes less memory than the traditional byte stream buffer (if printk_time is enabled). The record header is 16 bytes long, plus some padding bytes at the end if needed. The byte-stream buffer needed 3 chars for the syslog prefix, 15 char for the timestamp and a newline. - Buffer management is based on message sequence numbers. When records need to be discarded, the reading heads move on to the next full record. Unlike the byte-stream buffer, no old logged lines get truncated or partly overwritten by new ones. Sequence numbers also allow consumers of the log stream to get notified if any message in the stream they are about to read gets discarded during the time of reading. - Better buffered IO support for KERN_CONT continuation lines, when printk() is called multiple times for a single line. The use of KERN_CONT is now mandatory to use continuation; a few places in the kernel need trivial fixes here. The buffering could possibly be extended to per-cpu variables to allow better thread-safety for multiple printk() invocations for a single line. - Full-featured syslog facility value support. Different facilities can tag their messages. All userspace-injected messages enforce a facility value > 0 now, to be able to reliably distinguish them from the kernel-generated messages. Independent subsystems like a baseband processor running its own firmware, or a kernel-related userspace process can use their own unique facility values. Multiple independent log streams can co-exist that way in the same buffer. All share the same global sequence number counter to ensure proper ordering (and interleaving) and to allow the consumers of the log to reliably correlate the events from different facilities. Tested-by:

William Douglas <william.douglas@intel.com> Signed-off-by:

Kay Sievers <kay@vrfy.org> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/mem.c

+38 −17

Original line number	Diff line number	Diff line
		@@ -810,33 +810,54 @@ static const struct file_operations oldmem_fops = {
		static ssize_t kmsg_writev(struct kiocb iocb, const struct iovec iv,
		unsigned long count, loff_t pos)
		{
		char line, p;
		char buf, line;
		int i;
		ssize_t ret = -EFAULT;
		int level = default_message_loglevel;
		int facility = 1; /* LOG_USER */
		size_t len = iov_length(iv, count);
		ssize_t ret = len;

		line = kmalloc(len + 1, GFP_KERNEL);
		if (line == NULL)
		if (len > 1024)
		return -EINVAL;
		buf = kmalloc(len+1, GFP_KERNEL);
		if (buf == NULL)
		return -ENOMEM;

		/*
		* copy all vectors into a single string, to ensure we do
		* not interleave our log line with other printk calls
		*/
		p = line;
		line = buf;
		for (i = 0; i < count; i++) {
		if (copy_from_user(p, iv[i].iov_base, iv[i].iov_len))
		if (copy_from_user(line, iv[i].iov_base, iv[i].iov_len))
		goto out;
		p += iv[i].iov_len;
		line += iv[i].iov_len;
		}

		/*
		* Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
		* the decimal value represents 32bit, the lower 3 bit are the log
		* level, the rest are the log facility.
		*
		* If no prefix or no userspace facility is specified, we
		* enforce LOG_USER, to be able to reliably distinguish
		* kernel-generated messages from userspace-injected ones.
		*/
		line = buf;
		if (line[0] == '<') {
		char *endp = NULL;

		i = simple_strtoul(line+1, &endp, 10);
		if (endp && endp[0] == '>') {
		level = i & 7;
		if (i >> 3)
		facility = i >> 3;
		endp++;
		len -= endp - line;
		line = endp;
		}
		}
		p[0] = '\0';
		line[len] = '\0';

		ret = printk("%s", line);
		/* printk can add a prefix */
		if (ret > len)
		ret = len;
		printk_emit(facility, level, NULL, 0, "%s", line);
		out:
		kfree(line);
		kfree(buf);
		return ret;
		}

include/linux/printk.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -95,8 +95,19 @@ extern int printk_needs_cpu(int cpu);
		extern void printk_tick(void);

		#ifdef CONFIG_PRINTK
		asmlinkage __printf(5, 0)
		int vprintk_emit(int facility, int level,
		const char *dict, size_t dictlen,
		const char *fmt, va_list args);

		asmlinkage __printf(1, 0)
		int vprintk(const char *fmt, va_list args);

		asmlinkage __printf(5, 6) __cold
		asmlinkage int printk_emit(int facility, int level,
		const char *dict, size_t dictlen,
		const char *fmt, ...);

		asmlinkage __printf(1, 2) __cold
		int printk(const char *fmt, ...);

kernel/printk.c

+590 −424

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