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    Subject[PATCH 5/5] printk: rename LOG_NEWLINE and tidy up
    Date
    Rename LOG_NEWLINE to be LOG_COMPLETE, so it makes more sense in the
    context of a log record (or a string of them) rather than how a
    record gets formatted.

    Add a block of commentary explaining how the log flags indicate that
    consecutive log records should be treated as a single logical log
    entry.

    Do some other tidying of the code now that a lot of the former flags
    complexity has been eliminated.

    Signed-off-by: Alex Elder <elder@linaro.org>
    ---
    kernel/printk/printk.c | 73 +++++++++++++++++++++++++++++---------------------
    1 file changed, 42 insertions(+), 31 deletions(-)

    diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
    index bfc2581..69bfd39 100644
    --- a/kernel/printk/printk.c
    +++ b/kernel/printk/printk.c
    @@ -150,7 +150,7 @@ static int console_may_schedule;
    * are stored..
    *
    * If the heads indicate available messages, the length in the header
    - * tells the start next message. A length == 0 for the next message
    + * tells the start of the next message. A length == 0 for the next message
    * indicates a wrap-around to the beginning of the buffer.
    *
    * Every record carries the monotonic timestamp in microseconds, as well as
    @@ -159,6 +159,17 @@ static int console_may_schedule;
    * a matching syslog facility, by default LOG_USER. The origin of every
    * message can be reliably determined that way.
    *
    + * If a printk() call doesn't end in a newline, the content of the message
    + * is buffered temporarily so that a subsequent printk() call can be
    + * appended to it. Occasionally a buffered/partial message needs to be
    + * flushed to the log before the logically next printk() call is seen.
    + * This is distinguished in log records by the presence (or absence) of a
    + * LOG_COMPLETE flag. In this case the last log record comprising a
    + * the original message has LOG_COMPLETE set; the rest do not. When
    + * formatted, a log record will include a prefix (including a time stamp
    + * and possibly a syslog value) whenever its predecessor in the log was
    + * marked LOG_COMPLETE.
    + *
    * The human readable log message directly follows the message header. The
    * length of the message text is stored in the header, the stored message
    * is not terminated.
    @@ -209,7 +220,7 @@ static int console_may_schedule;

    enum log_flags {
    LOG_NOCONS = 1, /* already flushed, do not print to console */
    - LOG_NEWLINE = 2, /* text ended with a newline */
    + LOG_COMPLETE = 2, /* this record ends a log entry */
    };

    struct printk_log {
    @@ -432,7 +443,7 @@ static int log_store(int facility, int level, bool force_new,
    * the previous one to mark it complete.
    */
    if (force_new && log_last_msg)
    - log_last_msg->flags |= LOG_NEWLINE;
    + log_last_msg->flags |= LOG_COMPLETE;

    msg = (struct printk_log *)(log_buf + log_next_idx);
    memcpy(log_text(msg), text, text_len);
    @@ -632,9 +643,9 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
    * a record that should be merged with one or more earlier records.
    * And a '-' indicates a "normal" self-contained single record.
    */
    - if (!(user->prev & LOG_NEWLINE))
    + if (!(user->prev & LOG_COMPLETE))
    cont = '+';
    - else if (!(msg->flags & LOG_NEWLINE))
    + else if (!(msg->flags & LOG_COMPLETE))
    cont = 'c';
    else
    cont = '-';
    @@ -1015,15 +1026,9 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
    {
    const char *text = log_text(msg);
    size_t text_size = msg->text_len;
    - bool prefix = true;
    - bool newline = true;
    size_t len = 0;
    -
    - if (!(prev & LOG_NEWLINE))
    - prefix = false;
    -
    - if (!(msg->flags & LOG_NEWLINE))
    - newline = false;
    + bool prefix = !!(prev & LOG_COMPLETE);
    + bool newline = !!(msg->flags & LOG_COMPLETE);

    do {
    const char *next = memchr(text, '\n', text_size);
    @@ -1556,7 +1561,8 @@ static size_t cont_print_text(char *text, size_t size)
    size_t textlen = 0;
    size_t len;

    - if (cont.cons == 0 && (console_prev & LOG_NEWLINE)) {
    + /* If we're starting a new one, format a time stamp */
    + if (cont.cons == 0 && console_prev & LOG_COMPLETE) {
    textlen += print_time(cont.ts_nsec, text);
    size -= textlen;
    }
    @@ -1571,7 +1577,7 @@ static size_t cont_print_text(char *text, size_t size)
    }

    if (cont.flushed) {
    - if (cont.flags & LOG_NEWLINE)
    + if (cont.flags & LOG_COMPLETE)
    text[textlen++] = '\n';
    /* got everything, release buffer */
    cont.len = 0;
    @@ -1637,7 +1643,7 @@ asmlinkage int vprintk_emit(int facility, int level,
    recursion_bug = 0;
    text_len = strlen(recursion_msg);
    /* emit KERN_CRIT message */
    - printed_len += log_store(0, 2, true, LOG_NEWLINE, 0,
    + printed_len += log_store(0, 2, true, LOG_COMPLETE, 0,
    NULL, 0, recursion_msg, text_len);
    }

    @@ -1659,7 +1665,7 @@ asmlinkage int vprintk_emit(int facility, int level,
    */
    if (text_len && text[text_len-1] == '\n') {
    text_len--;
    - lflags = LOG_NEWLINE;
    + lflags = LOG_COMPLETE;
    }

    /* strip kernel syslog prefix and extract log level or control flags */
    @@ -1690,17 +1696,23 @@ asmlinkage int vprintk_emit(int facility, int level,

    if (dict) {
    force_new = true;
    - lflags = LOG_NEWLINE;
    + lflags = LOG_COMPLETE;
    }

    - if (!(lflags & LOG_NEWLINE)) {
    + /*
    + * If there's a partial record buffered by someone else
    + * we'll want to force a new entry to be started.
    + */
    + if (cont.len)
    + force_new |= cont.owner != current;
    + if (!(lflags & LOG_COMPLETE)) {
    /*
    * We're recording an incomplete record. We'll add it to the
    - * "cont" buffer if possible, but if it contains data written
    - * by somebody else we need to flush that to the log first.
    + * "cont" buffer if possible, but if we're forcing a new
    + * entry we need to flush the buffer to the log first.
    */
    - if (cont.len && (force_new || cont.owner != current))
    - cont_flush(LOG_NEWLINE);
    + if (cont.len && force_new)
    + cont_flush(LOG_COMPLETE);

    /* If we're unable to buffer it, store it immediately */
    if (cont_add(facility, level, text, text_len))
    @@ -1713,18 +1725,17 @@ asmlinkage int vprintk_emit(int facility, int level,
    bool stored = false;

    /*
    - * This record is complete (it should be formatted with a
    - * newline), so we'll be writing it to the log. If there
    - * are any incomplete records buffered we will need to
    - * flush those to the log first. If possible, we'll add
    - * this record to the buffer first. If there's nothing
    - * buffered, just write this record to the log.
    + * This record is complete, so we'll be writing it to the log.
    + * If there are any incomplete records buffered we'll try to
    + * add this record to the buffer before flushing it to the log.
    + * Otherwise if there's nothing buffered, just write this
    + * record to the log directly.
    */
    if (cont.len) {
    - if (cont.owner == current && !force_new)
    + if (!force_new)
    stored = cont_add(facility, level, text,
    text_len);
    - cont_flush(LOG_NEWLINE);
    + cont_flush(LOG_COMPLETE);
    }

    if (stored)
    --
    1.9.1


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