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kmsg: /proc/kmsg - support reading of partial log records 

Restore support for partial reads of any size on /proc/kmsg, in case the
supplied read buffer is smaller than the record size.

Some people seem to think is is ia good idea to run:
  $ dd if=/proc/kmsg bs=1 of=...
as a klog bridge.

Resolves-bug: https://bugzilla.kernel.org/show_bug.cgi?id=44211
Reported-by: Jukka Ollila <jiiksteri@gmail.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 2012-07-09 10:05:10 -07:00 committed by Greg Kroah-Hartman
parent 68b6507dc5
commit eb02dac937
1 changed files with 20 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
kernel/printk.c
View File

@ -217,6 +217,7 @@ static DEFINE_RAW_SPINLOCK(logbuf_lock);
/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
static u32 syslog_idx;
static size_t syslog_partial;
/* index and sequence number of the first record stored in the buffer */
static u64 log_first_seq;
@ -890,22 +891,33 @@ static int syslog_print(char __user *buf, int size)
while (size > 0) {
size_t n;
size_t skip;
raw_spin_lock_irq(&logbuf_lock);
if (syslog_seq < log_first_seq) {
/* messages are gone, move to first one */
syslog_seq = log_first_seq;
syslog_idx = log_first_idx;
syslog_partial = 0;
}
if (syslog_seq == log_next_seq) {
raw_spin_unlock_irq(&logbuf_lock);
break;
}
skip = syslog_partial;
msg = log_from_idx(syslog_idx);
n = msg_print_text(msg, true, text, LOG_LINE_MAX);
if (n <= size) {
if (n - syslog_partial <= size) {
/* message fits into buffer, move forward */
syslog_idx = log_next(syslog_idx);
syslog_seq++;
n -= syslog_partial;
syslog_partial = 0;
} else if (!len){
/* partial read(), remember position */
n = size;
syslog_partial += n;
} else
n = 0;
raw_spin_unlock_irq(&logbuf_lock);
@ -913,17 +925,15 @@ static int syslog_print(char __user *buf, int size)
if (!n)
break;
len += n;
size -= n;
buf += n;
n = copy_to_user(buf - n, text, n);
if (n) {
len -= n;
if (copy_to_user(buf, text + skip, n)) {
if (!len)
len = -EFAULT;
break;
}
len += n;
size -= n;
buf += n;
}
kfree(text);
@ -1107,6 +1117,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
/* messages are gone, move to first one */
syslog_seq = log_first_seq;
syslog_idx = log_first_idx;
syslog_partial = 0;
}
if (from_file) {
/*
@ -1129,6 +1140,7 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
idx = log_next(idx);
seq++;
}
error -= syslog_partial;
}
raw_spin_unlock_irq(&logbuf_lock);
break;