less: fix bugs discovered with "git log -p | less -m" on kernel tree

function                                             old     new   delta
read_lines                                           685     733     +48

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 24 insertions, 14 deletions

diff --git a/miscutils/less.c b/miscutils/less.c
index 574f222e0..36d0a0bd9 100644
--- a/miscutils/less.c
+++ b/miscutils/less.c
@@ -404,6 +404,9 @@ static void fill_match_lines(unsigned pos);
  * last_line_pos - screen line position of next char to be read
  *      (takes into account tabs and backspaces)
  * eof_error - < 0 error, == 0 EOF, > 0 not EOF/error
+ *
+ * "git log -p | less -m" on the kernel git tree is a good test for EAGAINs,
+ * "/search on very long input" and "reaching max line count" corner cases.
  */
 static void read_lines(void)
 {
@@ -414,9 +417,13 @@ static void read_lines(void)
 #if ENABLE_FEATURE_LESS_REGEXP
         unsigned old_max_fline = max_fline;
         time_t last_time = 0;
-        unsigned seconds_p1 = 3; /* seconds_to_loop + 1 */
+        int had_progress = 2;
 #endif
 
+        /* (careful: max_fline can be -1) */
+        if (max_fline + 1 > MAXLINES)
+                return;
+
         if (option_mask32 & FLAG_N)
                 w -= 8;
 
@@ -441,6 +448,7 @@ static void read_lines(void)
                         char c;
                         /* if no unprocessed chars left, eat more */
                         if (readpos >= readeof) {
+                                errno = 0;
                                 ndelay_on(0);
                                 eof_error = safe_read(STDIN_FILENO, readbuf, sizeof(readbuf));
                                 ndelay_off(0);
@@ -448,6 +456,7 @@ static void read_lines(void)
                                 readeof = eof_error;
                                 if (eof_error <= 0)
                                         goto reached_eof;
+                                had_progress = 1;
                         }
                         c = readbuf[readpos];
                         /* backspace? [needed for manpages] */
@@ -519,31 +528,23 @@ static void read_lines(void)
 #endif
                 }
                 if (eof_error <= 0) {
-                        if (eof_error < 0) {
-                                if (errno == EAGAIN) {
-                                        /* not yet eof or error, reset flag (or else
-                                         * we will hog CPU - select() will return
-                                         * immediately */
-                                        eof_error = 1;
-                                } else {
-                                        print_statusline(bb_msg_read_error);
-                                }
-                        }
 #if !ENABLE_FEATURE_LESS_REGEXP
                         break;
 #else
                         if (wanted_match < num_matches) {
                                 break;
-                        } else { /* goto_match called us */
+                        } /* else: goto_match() called us */
+                        if (errno == EAGAIN) {
                                 time_t t = time(NULL);
                                 if (t != last_time) {
                                         last_time = t;
-                                        if (--seconds_p1 == 0)
+                                        if (--had_progress < 0)
                                                 break;
                                 }
                                 sched_yield();
-                                goto again0; /* go loop again (max 2 seconds) */
+                                goto again0;
                         }
+                        break;
 #endif
                 }
                 max_fline++;
@@ -551,6 +552,15 @@ static void read_lines(void)
                 p = current_line;
                 last_line_pos = 0;
         } /* end of "read lines until we reach cur_fline" loop */
+
+        if (eof_error < 0) {
+                if (errno == EAGAIN) {
+                        eof_error = 1;
+                } else {
+                        print_statusline(bb_msg_read_error);
+                }
+        }
+
         fill_match_lines(old_max_fline);
 #if ENABLE_FEATURE_LESS_REGEXP
         /* prevent us from being stuck in search for a match */