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kmsg: export printk records to the /dev/kmsg interface

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Support for multiple concurrent readers of /dev/kmsg, with read(),
seek(), poll() support. Output of message sequence numbers, to allow
userspace log consumers to reliably reconnect and reconstruct their
state at any given time. After open("/dev/kmsg"), read() always
returns *all* buffered records. If only future messages should be
read, SEEK_END can be used. In case records get overwritten while
/dev/kmsg is held open, or records get faster overwritten than they
are read, the next read() will return -EPIPE and the current reading
position gets updated to the next available record. The passed
sequence numbers allow the log consumer to calculate the amount of
lost messages.

  [root@mop ~]# cat /dev/kmsg
  5,0,0;Linux version 3.4.0-rc1+ (kay@mop) (gcc version 4.7.0 20120315 ...
  6,159,423091;ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff])
  7,160,424069;pci_root PNP0A03:00: host bridge window [io  0x0000-0x0cf7] (ignored)
   SUBSYSTEM=acpi
   DEVICE=+acpi:PNP0A03:00
  6,339,5140900;NET: Registered protocol family 10
  30,340,5690716;udevd[80]: starting version 181
  6,341,6081421;FDC 0 is a S82078B
  6,345,6154686;microcode: CPU0 sig=0x623, pf=0x0, revision=0x0
  7,346,6156968;sr 1:0:0:0: Attached scsi CD-ROM sr0
   SUBSYSTEM=scsi
   DEVICE=+scsi:1:0:0:0
  6,347,6289375;microcode: CPU1 sig=0x623, pf=0x0, revision=0x0

Cc: Karel Zak <kzak@redhat.com>
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>
This commit is contained in:
Kay Sievers 2012-05-03 02:29:41 +02:00 committed by Greg Kroah-Hartman
parent 7ff9554bb5
commit e11fea92e1
3 changed files with 316 additions and 60 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

61
drivers/char/mem.c
View File

@ -807,65 +807,6 @@ static const struct file_operations oldmem_fops = {
};
#endif
static ssize_t kmsg_writev(struct kiocb *iocb, const struct iovec *iv,
unsigned long count, loff_t pos)
{
char *buf, *line;
int i;
int level = default_message_loglevel;
int facility = 1; /* LOG_USER */
size_t len = iov_length(iv, count);
ssize_t ret = len;
if (len > 1024)
return -EINVAL;
buf = kmalloc(len+1, GFP_KERNEL);
if (buf == NULL)
return -ENOMEM;
line = buf;
for (i = 0; i < count; i++) {
if (copy_from_user(line, iv[i].iov_base, iv[i].iov_len))
goto out;
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;
}
}
line[len] = '\0';
printk_emit(facility, level, NULL, 0, "%s", line);
out:
kfree(buf);
return ret;
}
static const struct file_operations kmsg_fops = {
.aio_write = kmsg_writev,
.llseek = noop_llseek,
};
static const struct memdev {
const char *name;
umode_t mode;
@ -884,7 +825,7 @@ static const struct memdev {
[7] = { "full", 0666, &full_fops, NULL },
[8] = { "random", 0666, &random_fops, NULL },
[9] = { "urandom", 0666, &urandom_fops, NULL },
[11] = { "kmsg", 0, &kmsg_fops, NULL },
[11] = { "kmsg", 0644, &kmsg_fops, NULL },
#ifdef CONFIG_CRASH_DUMP
[12] = { "oldmem", 0, &oldmem_fops, NULL },
#endif

2
include/linux/printk.h
View File

@ -300,6 +300,8 @@ extern void dump_stack(void) __cold;
no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#endif
extern const struct file_operations kmsg_fops;
enum {
DUMP_PREFIX_NONE,
DUMP_PREFIX_ADDRESS,

313
kernel/printk.c
View File

@ -41,6 +41,7 @@
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/rculist.h>
#include <linux/poll.h>
#include <asm/uaccess.h>
@ -149,6 +150,48 @@ static int console_may_schedule;
* length of the message text is stored in the header, the stored message
* is not terminated.
*
* Optionally, a message can carry a dictionary of properties (key/value pairs),
* to provide userspace with a machine-readable message context.
*
* Examples for well-defined, commonly used property names are:
* DEVICE=b12:8 device identifier
* b12:8 block dev_t
* c127:3 char dev_t
* n8 netdev ifindex
* +sound:card0 subsystem:devname
* SUBSYSTEM=pci driver-core subsystem name
*
* Valid characters in property names are [a-zA-Z0-9.-_]. The plain text value
* follows directly after a '=' character. Every property is terminated by
* a '\0' character. The last property is not terminated.
*
* Example of a message structure:
* 0000 ff 8f 00 00 00 00 00 00 monotonic time in nsec
* 0008 34 00 record is 52 bytes long
* 000a 0b 00 text is 11 bytes long
* 000c 1f 00 dictionary is 23 bytes long
* 000e 03 00 LOG_KERN (facility) LOG_ERR (level)
* 0010 69 74 27 73 20 61 20 6c "it's a l"
* 69 6e 65 "ine"
* 001b 44 45 56 49 43 "DEVIC"
* 45 3d 62 38 3a 32 00 44 "E=b8:2\0D"
* 52 49 56 45 52 3d 62 75 "RIVER=bu"
* 67 "g"
* 0032 00 00 00 padding to next message header
*
* The 'struct log' buffer header must never be directly exported to
* userspace, it is a kernel-private implementation detail that might
* need to be changed in the future, when the requirements change.
*
* /dev/kmsg exports the structured data in the following line format:
* "level,sequnum,timestamp;<message text>\n"
*
* The optional key/value pairs are attached as continuation lines starting
* with a space character and terminated by a newline. All possible
* non-prinatable characters are escaped in the "\xff" notation.
*
* Users of the export format should ignore possible additional values
* separated by ',', and find the message after the ';' character.
*/
struct log {
@ -297,6 +340,276 @@ static void log_store(int facility, int level,
log_next_seq++;
}
/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
u64 seq;
u32 idx;
struct mutex lock;
char buf[8192];
};
static ssize_t devkmsg_writev(struct kiocb *iocb, const struct iovec *iv,
unsigned long count, loff_t pos)
{
char *buf, *line;
int i;
int level = default_message_loglevel;
int facility = 1; /* LOG_USER */
size_t len = iov_length(iv, count);
ssize_t ret = len;
if (len > LOG_LINE_MAX)
return -EINVAL;
buf = kmalloc(len+1, GFP_KERNEL);
if (buf == NULL)
return -ENOMEM;
line = buf;
for (i = 0; i < count; i++) {
if (copy_from_user(line, iv[i].iov_base, iv[i].iov_len))
goto out;
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;
}
}
line[len] = '\0';
printk_emit(facility, level, NULL, 0, "%s", line);
out:
kfree(buf);
return ret;
}
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 log *msg;
size_t i;
size_t len;
ssize_t ret;
if (!user)
return -EBADF;
mutex_lock(&user->lock);
raw_spin_lock(&logbuf_lock);
while (user->seq == log_next_seq) {
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
raw_spin_unlock(&logbuf_lock);
goto out;
}
raw_spin_unlock(&logbuf_lock);
ret = wait_event_interruptible(log_wait,
user->seq != log_next_seq);
if (ret)
goto out;
raw_spin_lock(&logbuf_lock);
}
if (user->seq < log_first_seq) {
/* our last seen message is gone, return error and reset */
user->idx = log_first_idx;
user->seq = log_first_seq;
ret = -EPIPE;
raw_spin_unlock(&logbuf_lock);
goto out;
}
msg = log_from_idx(user->idx);
len = sprintf(user->buf, "%u,%llu,%llu;",
msg->level, user->seq, msg->ts_nsec / 1000);
/* escape non-printable characters */
for (i = 0; i < msg->text_len; i++) {
char c = log_text(msg)[i];
if (c < ' ' || c >= 128)
len += sprintf(user->buf + len, "\\x%02x", c);
else
user->buf[len++] = c;
}
user->buf[len++] = '\n';
if (msg->dict_len) {
bool line = true;
for (i = 0; i < msg->dict_len; i++) {
char c = log_dict(msg)[i];
if (line) {
user->buf[len++] = ' ';
line = false;
}
if (c == '\0') {
user->buf[len++] = '\n';
line = true;
continue;
}
if (c < ' ' || c >= 128) {
len += sprintf(user->buf + len, "\\x%02x", c);
continue;
}
user->buf[len++] = c;
}
user->buf[len++] = '\n';
}
user->idx = log_next(user->idx);
user->seq++;
raw_spin_unlock(&logbuf_lock);
if (len > count) {
ret = -EINVAL;
goto out;
}
if (copy_to_user(buf, user->buf, len)) {
ret = -EFAULT;
goto out;
}
ret = len;
out:
mutex_unlock(&user->lock);
return ret;
}
static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
{
struct devkmsg_user *user = file->private_data;
loff_t ret = 0;
if (!user)
return -EBADF;
if (offset)
return -ESPIPE;
raw_spin_lock(&logbuf_lock);
switch (whence) {
case SEEK_SET:
/* the first record */
user->idx = log_first_idx;
user->seq = log_first_seq;
break;
case SEEK_DATA:
/*
* The first record after the last SYSLOG_ACTION_CLEAR,
* like issued by 'dmesg -c'. Reading /dev/kmsg itself
* changes no global state, and does not clear anything.
*/
user->idx = clear_idx;
user->seq = clear_seq;
break;
case SEEK_END:
/* after the last record */
user->idx = log_next_idx;
user->seq = log_next_seq;
break;
default:
ret = -EINVAL;
}
raw_spin_unlock(&logbuf_lock);
return ret;
}
static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
{
struct devkmsg_user *user = file->private_data;
int ret = 0;
if (!user)
return POLLERR|POLLNVAL;
poll_wait(file, &log_wait, wait);
raw_spin_lock(&logbuf_lock);
if (user->seq < log_next_seq) {
/* return error when data has vanished underneath us */
if (user->seq < log_first_seq)
ret = POLLIN|POLLRDNORM|POLLERR|POLLPRI;
ret = POLLIN|POLLRDNORM;
}
raw_spin_unlock(&logbuf_lock);
return ret;
}
static int devkmsg_open(struct inode *inode, struct file *file)
{
struct devkmsg_user *user;
int err;
/* write-only does not need any file context */
if ((file->f_flags & O_ACCMODE) == O_WRONLY)
return 0;
err = security_syslog(SYSLOG_ACTION_READ_ALL);
if (err)
return err;
user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
if (!user)
return -ENOMEM;
mutex_init(&user->lock);
raw_spin_lock(&logbuf_lock);
user->idx = log_first_idx;
user->seq = log_first_seq;
raw_spin_unlock(&logbuf_lock);
file->private_data = user;
return 0;
}
static int devkmsg_release(struct inode *inode, struct file *file)
{
struct devkmsg_user *user = file->private_data;
if (!user)
return 0;
mutex_destroy(&user->lock);
kfree(user);
return 0;
}
const struct file_operations kmsg_fops = {
.open = devkmsg_open,
.read = devkmsg_read,
.aio_write = devkmsg_writev,
.llseek = devkmsg_llseek,
.poll = devkmsg_poll,
.release = devkmsg_release,
};
#ifdef CONFIG_KEXEC
/*
* This appends the listed symbols to /proc/vmcoreinfo