Fix apparent garbage in the message buffer.
While we have had a fix in place (options PRINTF_BUFR_SIZE=128) to fix scrambled console output, the message buffer and syslog were still getting log messages one character at a time. While all of the characters still made it into the log (courtesy of atomic operations), they were often interleaved when there were multiple threads writing to the buffer at the same time. This fixes message buffer accesses to use buffering logic as well, so that strings that are less than PRINTF_BUFR_SIZE will be put into the message buffer atomically. So now dmesg output should look the same as console output. subr_msgbuf.c: Convert most message buffer calls to use a new spin lock instead of atomic variables in some places. Add a new routine, msgbuf_addstr(), that adds a NUL-terminated string to a message buffer. This takes a priority argument, which allows us to eliminate some races (at least in the the string at a time case) that are present in the implementation of msglogchar(). (dangling and lastpri are static variables, and are subject to races when multiple callers are present.) msgbuf_addstr() also allows the caller to request that carriage returns be stripped out of the string. This matches the behavior of msglogchar(), but in testing so far it doesn't appear that any newlines are being stripped out. So the carriage return removal functionality may be a candidate for removal later on if further analysis shows that it isn't necessary. subr_prf.c: Add a new msglogstr() routine that calls msgbuf_logstr(). Rename putcons() to putbuf(). This now handles buffered output to the message log as well as the console. Also, remove the logic in putcons() (now putbuf()) that added a carriage return before a newline. The console path was the only path that needed it, and cnputc() (called by cnputs()) already adds a carriage return. So this duplication resulted in kernel-generated console output lines ending in '\r''\r''\n'. Refactor putchar() to handle the new buffering scheme. Add buffering to log(). Change log_console() to use msglogstr() instead of msglogchar(). Don't add extra newlines by default in log_console(). Hide that behavior behind a tunable/sysctl (kern.log_console_add_linefeed) for those who would like the old behavior. The old behavior led to the insertion of extra newlines for log output for programs that print out a string, and then a trailing newline on a separate write. (This is visible with dmesg -a.) msgbuf.h: Add a prototype for msgbuf_addstr(). Add three new fields to struct msgbuf, msg_needsnl, msg_lastpri and msg_lock. The first two are needed for log message functionality previously handled by msglogchar(). (Which is still active if buffering isn't enabled.) Include sys/lock.h and sys/mutex.h for the new mutex. Reviewed by: gibbs
This commit is contained in:
Kenneth D. Merry
parent
1d6fbefd90
commit
d42a4eb507
@ -31,8 +31,16 @@
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/lock.h>
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#include <sys/mutex.h>
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#include <sys/msgbuf.h>
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/*
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* Maximum number conversion buffer length: uintmax_t in base 2, plus <>
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* around the priority, and a terminating NUL.
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*/
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#define MAXPRIBUF (sizeof(intmax_t) * NBBY + 3)
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/* Read/write sequence numbers are modulo a multiple of the buffer size. */
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#define SEQMOD(size) ((size) * 16)
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@ -51,6 +59,9 @@ msgbuf_init(struct msgbuf *mbp, void *ptr, int size)
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mbp->msg_seqmod = SEQMOD(size);
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msgbuf_clear(mbp);
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mbp->msg_magic = MSG_MAGIC;
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mbp->msg_lastpri = -1;
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mbp->msg_needsnl = 0;
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mtx_init(&mbp->msg_lock, "msgbuf", NULL, MTX_SPIN);
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}
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/*
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@ -80,6 +91,11 @@ msgbuf_reinit(struct msgbuf *mbp, void *ptr, int size)
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}
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msgbuf_clear(mbp);
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}
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mbp->msg_lastpri = -1;
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/* Assume that the old message buffer didn't end in a newline. */
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mbp->msg_needsnl = 1;
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mtx_init(&mbp->msg_lock, "msgbuf", NULL, MTX_SPIN);
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}
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/*
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@ -110,25 +126,140 @@ msgbuf_getcount(struct msgbuf *mbp)
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}
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/*
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* Append a character to a message buffer. This function can be
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* considered fully reentrant so long as the number of concurrent
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* callers is less than the number of characters in the buffer.
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* However, the message buffer is only guaranteed to be consistent
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* for reading when there are no callers in this function.
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* Add a character into the message buffer, and update the checksum and
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* sequence number.
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*
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* The caller should hold the message buffer spinlock.
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*/
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static inline void
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msgbuf_do_addchar(struct msgbuf *mbp, u_int *seq, int c)
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{
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u_int pos;
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/* Make sure we properly wrap the sequence number. */
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pos = MSGBUF_SEQ_TO_POS(mbp, *seq);
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mbp->msg_cksum += (u_int)c -
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(u_int)(u_char)mbp->msg_ptr[pos];
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mbp->msg_ptr[pos] = c;
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*seq = MSGBUF_SEQNORM(mbp, *seq + 1);
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}
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/*
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* Append a character to a message buffer.
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*/
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void
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msgbuf_addchar(struct msgbuf *mbp, int c)
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{
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u_int new_seq, pos, seq;
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mtx_lock_spin(&mbp->msg_lock);
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do {
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msgbuf_do_addchar(mbp, &mbp->msg_wseq, c);
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mtx_unlock_spin(&mbp->msg_lock);
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}
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/*
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* Append a NUL-terminated string with a priority to a message buffer.
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* Filter carriage returns if the caller requests it.
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*
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* XXX The carriage return filtering behavior is present in the
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* msglogchar() API, however testing has shown that we don't seem to send
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* carriage returns down this path. So do we still need it?
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*/
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void
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msgbuf_addstr(struct msgbuf *mbp, int pri, char *str, int filter_cr)
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{
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u_int seq;
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size_t len, prefix_len;
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char prefix[MAXPRIBUF];
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int nl, i;
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len = strlen(str);
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prefix_len = 0;
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nl = 0;
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/* If we have a zero-length string, no need to do anything. */
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if (len == 0)
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return;
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mtx_lock_spin(&mbp->msg_lock);
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/*
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* If this is true, we may need to insert a new priority sequence,
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* so prepare the prefix.
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*/
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if (pri != -1)
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prefix_len = sprintf(prefix, "<%d>", pri);
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/*
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* Starting write sequence number.
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*/
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seq = mbp->msg_wseq;
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new_seq = MSGBUF_SEQNORM(mbp, seq + 1);
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} while (atomic_cmpset_rel_int(&mbp->msg_wseq, seq, new_seq) == 0);
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pos = MSGBUF_SEQ_TO_POS(mbp, seq);
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atomic_add_int(&mbp->msg_cksum, (u_int)(u_char)c -
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(u_int)(u_char)mbp->msg_ptr[pos]);
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mbp->msg_ptr[pos] = c;
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/*
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* Whenever there is a change in priority, we have to insert a
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* newline, and a priority prefix if the priority is not -1. Here
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* we detect whether there was a priority change, and whether we
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* did not end with a newline. If that is the case, we need to
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* insert a newline before this string.
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*/
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if (mbp->msg_lastpri != pri && mbp->msg_needsnl != 0) {
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msgbuf_do_addchar(mbp, &seq, '\n');
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mbp->msg_needsnl = 0;
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}
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for (i = 0; i < len; i++) {
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/*
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* If we just had a newline, and the priority is not -1
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* (and therefore prefix_len != 0), then we need a priority
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* prefix for this line.
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*/
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if (mbp->msg_needsnl == 0 && prefix_len != 0) {
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int j;
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for (j = 0; j < prefix_len; j++)
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msgbuf_do_addchar(mbp, &seq, prefix[j]);
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}
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/*
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* Don't copy carriage returns if the caller requested
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* filtering.
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*
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* XXX This matches the behavior of msglogchar(), but is it
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* necessary? Testing has shown that we don't seem to get
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* carriage returns here.
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*/
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if ((filter_cr != 0) && (str[i] == '\r'))
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continue;
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/*
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* Clear this flag if we see a newline. This affects whether
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* we need to insert a new prefix or insert a newline later.
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*/
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if (str[i] == '\n')
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mbp->msg_needsnl = 0;
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else
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mbp->msg_needsnl = 1;
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msgbuf_do_addchar(mbp, &seq, str[i]);
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}
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/*
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* Update the write sequence number for the actual number of
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* characters we put in the message buffer. (Depends on whether
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* carriage returns are filtered.)
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*/
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mbp->msg_wseq = seq;
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/*
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* Set the last priority.
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*/
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mbp->msg_lastpri = pri;
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mtx_unlock_spin(&mbp->msg_lock);
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}
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/*
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@ -141,14 +272,21 @@ msgbuf_getchar(struct msgbuf *mbp)
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u_int len, wseq;
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int c;
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mtx_lock_spin(&mbp->msg_lock);
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wseq = mbp->msg_wseq;
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len = MSGBUF_SEQSUB(mbp, wseq, mbp->msg_rseq);
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if (len == 0)
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if (len == 0) {
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mtx_unlock_spin(&mbp->msg_lock);
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return (-1);
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}
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if (len > mbp->msg_size)
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mbp->msg_rseq = MSGBUF_SEQNORM(mbp, wseq - mbp->msg_size);
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c = (u_char)mbp->msg_ptr[MSGBUF_SEQ_TO_POS(mbp, mbp->msg_rseq)];
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mbp->msg_rseq = MSGBUF_SEQNORM(mbp, mbp->msg_rseq + 1);
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mtx_unlock_spin(&mbp->msg_lock);
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return (c);
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}
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@ -161,10 +299,14 @@ msgbuf_getbytes(struct msgbuf *mbp, char *buf, int buflen)
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{
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u_int len, pos, wseq;
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mtx_lock_spin(&mbp->msg_lock);
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wseq = mbp->msg_wseq;
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len = MSGBUF_SEQSUB(mbp, wseq, mbp->msg_rseq);
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if (len == 0)
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if (len == 0) {
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mtx_unlock_spin(&mbp->msg_lock);
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return (0);
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}
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if (len > mbp->msg_size) {
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mbp->msg_rseq = MSGBUF_SEQNORM(mbp, wseq - mbp->msg_size);
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len = mbp->msg_size;
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@ -175,6 +317,9 @@ msgbuf_getbytes(struct msgbuf *mbp, char *buf, int buflen)
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bcopy(&mbp->msg_ptr[pos], buf, len);
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mbp->msg_rseq = MSGBUF_SEQNORM(mbp, mbp->msg_rseq + len);
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mtx_unlock_spin(&mbp->msg_lock);
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return (len);
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}
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@ -193,16 +338,21 @@ msgbuf_peekbytes(struct msgbuf *mbp, char *buf, int buflen, u_int *seqp)
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{
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u_int len, pos, wseq;
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mtx_lock_spin(&mbp->msg_lock);
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if (buf == NULL) {
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/* Just initialise *seqp. */
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*seqp = MSGBUF_SEQNORM(mbp, mbp->msg_wseq - mbp->msg_size);
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mtx_unlock_spin(&mbp->msg_lock);
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return (0);
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}
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wseq = mbp->msg_wseq;
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len = MSGBUF_SEQSUB(mbp, wseq, *seqp);
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if (len == 0)
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if (len == 0) {
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mtx_unlock_spin(&mbp->msg_lock);
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return (0);
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}
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if (len > mbp->msg_size) {
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*seqp = MSGBUF_SEQNORM(mbp, wseq - mbp->msg_size);
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len = mbp->msg_size;
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@ -212,6 +362,9 @@ msgbuf_peekbytes(struct msgbuf *mbp, char *buf, int buflen, u_int *seqp)
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len = min(len, (u_int)buflen);
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bcopy(&mbp->msg_ptr[MSGBUF_SEQ_TO_POS(mbp, *seqp)], buf, len);
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*seqp = MSGBUF_SEQNORM(mbp, *seqp + len);
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mtx_unlock_spin(&mbp->msg_lock);
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return (len);
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}
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@ -94,6 +94,7 @@ struct snprintf_arg {
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extern int log_open;
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static void msglogchar(int c, int pri);
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static void msglogstr(char *str, int pri, int filter_cr);
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static void putchar(int ch, void *arg);
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static char *ksprintn(char *nbuf, uintmax_t num, int base, int *len, int upper);
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static void snprintf_func(int ch, void *arg);
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@ -106,6 +107,14 @@ TUNABLE_INT("kern.log_console_output", &log_console_output);
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SYSCTL_INT(_kern, OID_AUTO, log_console_output, CTLFLAG_RW,
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&log_console_output, 0, "Duplicate console output to the syslog.");
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/*
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* See the comment in log_console() below for more explanation of this.
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*/
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static int log_console_add_linefeed = 0;
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TUNABLE_INT("kern.log_console_add_linefeed", &log_console_add_linefeed);
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SYSCTL_INT(_kern, OID_AUTO, log_console_add_linefeed, CTLFLAG_RW,
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&log_console_add_linefeed, 0, "log_console() adds extra newlines.");
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static int always_console_output = 0;
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TUNABLE_INT("kern.always_console_output", &always_console_output);
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SYSCTL_INT(_kern, OID_AUTO, always_console_output, CTLFLAG_RW,
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@ -240,16 +249,37 @@ log(int level, const char *fmt, ...)
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{
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va_list ap;
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struct putchar_arg pca;
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#ifdef PRINTF_BUFR_SIZE
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char bufr[PRINTF_BUFR_SIZE];
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#endif
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pca.tty = NULL;
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pca.pri = level;
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pca.flags = log_open ? TOLOG : TOCONS;
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#ifdef PRINTF_BUFR_SIZE
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pca.p_bufr = bufr;
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pca.p_next = pca.p_bufr;
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pca.n_bufr = sizeof(bufr);
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pca.remain = sizeof(bufr);
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*pca.p_next = '\0';
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#else
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pca.p_bufr = NULL;
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#endif
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va_start(ap, fmt);
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kvprintf(fmt, putchar, &pca, 10, ap);
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va_end(ap);
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#ifdef PRINTF_BUFR_SIZE
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/* Write any buffered console/log output: */
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if (*pca.p_bufr != '\0') {
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if (pca.flags & TOLOG)
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msglogstr(pca.p_bufr, level, /*filter_cr*/1);
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if (pca.flags & TOCONS)
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cnputs(pca.p_bufr);
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}
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#endif
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msgbuftrigger = 1;
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}
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@ -258,7 +288,7 @@ log(int level, const char *fmt, ...)
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void
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log_console(struct uio *uio)
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{
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int c, i, error, nl;
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int c, error, nl;
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char *consbuffer;
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int pri;
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@ -271,20 +301,48 @@ log_console(struct uio *uio)
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nl = 0;
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while (uio->uio_resid > 0) {
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c = imin(uio->uio_resid, CONSCHUNK);
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c = imin(uio->uio_resid, CONSCHUNK - 1);
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error = uiomove(consbuffer, c, uio);
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if (error != 0)
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break;
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for (i = 0; i < c; i++) {
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msglogchar(consbuffer[i], pri);
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if (consbuffer[i] == '\n')
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/* Make sure we're NUL-terminated */
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consbuffer[c] = '\0';
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if (consbuffer[c - 1] == '\n')
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nl = 1;
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else
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nl = 0;
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msglogstr(consbuffer, pri, /*filter_cr*/ 1);
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}
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/*
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* The previous behavior in log_console() is preserved when
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* log_console_add_linefeed is non-zero. For that behavior, if an
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* individual console write came in that was not terminated with a
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* line feed, it would add a line feed.
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*
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* This results in different data in the message buffer than
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* appears on the system console (which doesn't add extra line feed
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* characters).
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*
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* A number of programs and rc scripts write a line feed, or a period
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* and a line feed when they have completed their operation. On
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* the console, this looks seamless, but when displayed with
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* 'dmesg -a', you wind up with output that looks like this:
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*
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* Updating motd:
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* .
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*
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* On the console, it looks like this:
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* Updating motd:.
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*
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* We could add logic to detect that situation, or just not insert
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* the extra newlines. Set the kern.log_console_add_linefeed
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* sysctl/tunable variable to get the old behavior.
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*/
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if (!nl && log_console_add_linefeed) {
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consbuffer[0] = '\n';
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consbuffer[1] = '\0';
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msglogstr(consbuffer, pri, /*filter_cr*/ 1);
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}
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if (!nl)
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msglogchar('\n', pri);
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msgbuftrigger = 1;
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free(uio, M_IOV);
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free(consbuffer, M_TEMP);
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@ -330,9 +388,11 @@ vprintf(const char *fmt, va_list ap)
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retval = kvprintf(fmt, putchar, &pca, 10, ap);
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#ifdef PRINTF_BUFR_SIZE
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/* Write any buffered console output: */
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if (*pca.p_bufr != '\0')
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/* Write any buffered console/log output: */
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if (*pca.p_bufr != '\0') {
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cnputs(pca.p_bufr);
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msglogstr(pca.p_bufr, pca.pri, /*filter_cr*/ 1);
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}
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#endif
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if (!panicstr)
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@ -342,18 +402,18 @@ vprintf(const char *fmt, va_list ap)
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}
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static void
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putcons(int c, struct putchar_arg *ap)
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putbuf(int c, struct putchar_arg *ap)
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{
|
||||
/* Check if no console output buffer was provided. */
|
||||
if (ap->p_bufr == NULL)
|
||||
if (ap->p_bufr == NULL) {
|
||||
/* Output direct to the console. */
|
||||
if (ap->flags & TOCONS)
|
||||
cnputc(c);
|
||||
else {
|
||||
|
||||
if (ap->flags & TOLOG)
|
||||
msglogchar(c, ap->pri);
|
||||
} else {
|
||||
/* Buffer the character: */
|
||||
if (c == '\n') {
|
||||
*ap->p_next++ = '\r';
|
||||
ap->remain--;
|
||||
}
|
||||
*ap->p_next++ = c;
|
||||
ap->remain--;
|
||||
|
||||
@ -361,12 +421,35 @@ putcons(int c, struct putchar_arg *ap)
|
||||
*ap->p_next = '\0';
|
||||
|
||||
/* Check if the buffer needs to be flushed. */
|
||||
if (ap->remain < 3 || c == '\n') {
|
||||
if (ap->remain == 2 || c == '\n') {
|
||||
|
||||
if (ap->flags & TOLOG)
|
||||
msglogstr(ap->p_bufr, ap->pri, /*filter_cr*/1);
|
||||
|
||||
if (ap->flags & TOCONS) {
|
||||
if ((panicstr == NULL) && (constty != NULL))
|
||||
msgbuf_addstr(&consmsgbuf, -1,
|
||||
ap->p_bufr, /*filter_cr*/ 0);
|
||||
|
||||
if ((constty == NULL) ||(always_console_output))
|
||||
cnputs(ap->p_bufr);
|
||||
}
|
||||
|
||||
ap->p_next = ap->p_bufr;
|
||||
ap->remain = ap->n_bufr;
|
||||
*ap->p_next = '\0';
|
||||
}
|
||||
|
||||
/*
|
||||
* Since we fill the buffer up one character at a time,
|
||||
* this should not happen. We should always catch it when
|
||||
* ap->remain == 2 (if not sooner due to a newline), flush
|
||||
* the buffer and move on. One way this could happen is
|
||||
* if someone sets PRINTF_BUFR_SIZE to 1 or something
|
||||
* similarly silly.
|
||||
*/
|
||||
KASSERT(ap->remain > 2, ("Bad buffer logic, remain = %zd",
|
||||
ap->remain));
|
||||
}
|
||||
}
|
||||
|
||||
@ -381,26 +464,25 @@ putchar(int c, void *arg)
|
||||
struct putchar_arg *ap = (struct putchar_arg*) arg;
|
||||
struct tty *tp = ap->tty;
|
||||
int flags = ap->flags;
|
||||
int putbuf_done = 0;
|
||||
|
||||
/* Don't use the tty code after a panic or while in ddb. */
|
||||
if (kdb_active) {
|
||||
if (c != '\0')
|
||||
cnputc(c);
|
||||
} else if (panicstr || ((flags & TOCONS) && constty == NULL)) {
|
||||
if (c != '\0')
|
||||
putcons(c, ap);
|
||||
} else {
|
||||
if ((flags & TOTTY) && tp != NULL)
|
||||
if ((panicstr == NULL) && (flags & TOTTY) && (tp != NULL))
|
||||
tty_putchar(tp, c);
|
||||
|
||||
if (flags & TOCONS) {
|
||||
if (constty != NULL)
|
||||
msgbuf_addchar(&consmsgbuf, c);
|
||||
if (always_console_output && c != '\0')
|
||||
putcons(c, ap);
|
||||
putbuf(c, ap);
|
||||
putbuf_done = 1;
|
||||
}
|
||||
}
|
||||
if ((flags & TOLOG))
|
||||
msglogchar(c, ap->pri);
|
||||
if ((flags & TOLOG) && (putbuf_done == 0)) {
|
||||
if (c != '\0')
|
||||
putbuf(c, ap);
|
||||
}
|
||||
}
|
||||
|
||||
/*
|
||||
@ -890,6 +972,15 @@ msglogchar(int c, int pri)
|
||||
}
|
||||
}
|
||||
|
||||
static void
|
||||
msglogstr(char *str, int pri, int filter_cr)
|
||||
{
|
||||
if (!msgbufmapped)
|
||||
return;
|
||||
|
||||
msgbuf_addstr(msgbufp, pri, str, filter_cr);
|
||||
}
|
||||
|
||||
void
|
||||
msgbufinit(void *ptr, int size)
|
||||
{
|
||||
|
||||
@ -33,6 +33,9 @@
|
||||
#ifndef _SYS_MSGBUF_H_
|
||||
#define _SYS_MSGBUF_H_
|
||||
|
||||
#include <sys/lock.h>
|
||||
#include <sys/mutex.h>
|
||||
|
||||
struct msgbuf {
|
||||
char *msg_ptr; /* pointer to buffer */
|
||||
#define MSG_MAGIC 0x063062
|
||||
@ -42,6 +45,9 @@ struct msgbuf {
|
||||
u_int msg_rseq; /* read sequence number */
|
||||
u_int msg_cksum; /* checksum of contents */
|
||||
u_int msg_seqmod; /* range for sequence numbers */
|
||||
int msg_lastpri; /* saved priority value */
|
||||
int msg_needsnl; /* set when newline needed */
|
||||
struct mtx msg_lock; /* mutex to protect the buffer */
|
||||
};
|
||||
|
||||
/* Normalise a sequence number or a difference between sequence numbers. */
|
||||
@ -59,6 +65,7 @@ extern struct mtx msgbuf_lock;
|
||||
|
||||
void msgbufinit(void *ptr, int size);
|
||||
void msgbuf_addchar(struct msgbuf *mbp, int c);
|
||||
void msgbuf_addstr(struct msgbuf *mbp, int pri, char *str, int filter_cr);
|
||||
void msgbuf_clear(struct msgbuf *mbp);
|
||||
void msgbuf_copy(struct msgbuf *src, struct msgbuf *dst);
|
||||
int msgbuf_getbytes(struct msgbuf *mbp, char *buf, int buflen);
|
||||
|
||||
Loading…
Reference in New Issue
Block a user