less: improve regular file detection in line counting code

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

1 files changed, 28 insertions, 19 deletions

diff --git a/miscutils/less.c b/miscutils/less.c
index b38fcf766..be8d20e66 100644
--- a/miscutils/less.c
+++ b/miscutils/less.c
@@ -165,12 +165,6 @@ enum {
 enum { pattern_valid = 0 };
 #endif
 
-enum {
-        READING_FILE = -1,
-        READING_STDIN = -2,
-        READING_NONREG = -3
-};
-
 struct globals {
         int cur_fline; /* signed */
         int kbd_fd;  /* fd to get input from */
@@ -195,7 +189,10 @@ struct globals {
         char *filename;
         char **files;
 #if ENABLE_FEATURE_LESS_FLAGS
-        int num_lines; /* input source if < 0, line count if >= 0 */
+        int num_lines; /* a flag if < 0, line count if >= 0 */
+# define REOPEN_AND_COUNT (-1)
+# define REOPEN_STDIN     (-2)
+# define NOT_REGULAR_FILE (-3)
 #endif
 #if ENABLE_FEATURE_LESS_MARKS
         unsigned num_marks;
@@ -622,14 +619,29 @@ static void update_num_lines(void)
         char buf[4096];
 
         /* only do this for regular files */
-        if (num_lines == READING_FILE) {
+        if (num_lines != NOT_REGULAR_FILE) {
                 count = 0;
-                fd = open(filename, O_RDONLY);
+                fd = open("/proc/self/fd/0", O_RDONLY);
+                if (fd < 0 && num_lines == REOPEN_AND_COUNT) {
+                        /* "filename" is valid only if REOPEN_AND_COUNT */
+                        fd = open(filename, O_RDONLY);
+                }
                 if (fd < 0) {
                         /* somebody stole my file! */
-                        num_lines = READING_NONREG;
+                        num_lines = NOT_REGULAR_FILE;
                         return;
                 }
+#if ENABLE_FEATURE_LESS_FLAGS
+                {
+                        struct stat stbuf;
+                        if (fstat(fd, &stbuf) != 0
+                         || !S_ISREG(stbuf.st_mode)
+                        ) {
+                                num_lines = NOT_REGULAR_FILE;
+                                goto do_close;
+                        }
+                }
+#endif
                 while ((len = safe_read(fd, buf, sizeof(buf))) > 0) {
                         for (i = 0; i < len; ++i) {
                                 if (buf[i] == '\n' && ++count == MAXLINES)
@@ -638,6 +650,7 @@ static void update_num_lines(void)
                 }
  done:
                 num_lines = count;
+ do_close:
                 close(fd);
         }
 }
@@ -991,18 +1004,17 @@ static void buffer_lineno(int lineno)
 static void open_file_and_read_lines(void)
 {
         if (filename) {
+                xmove_fd(xopen(filename, O_RDONLY), STDIN_FILENO);
 #if ENABLE_FEATURE_LESS_FLAGS
-                struct stat stbuf;
-
-                xstat(filename, &stbuf);
-                if (!S_ISREG(stbuf.st_mode))
-                        num_lines = READING_NONREG;
+                num_lines = REOPEN_AND_COUNT;
 #endif
-                xmove_fd(xopen(filename, O_RDONLY), STDIN_FILENO);
         } else {
                 /* "less" with no arguments in argv[] */
                 /* For status line only */
                 filename = xstrdup(bb_msg_standard_input);
+#if ENABLE_FEATURE_LESS_FLAGS
+                num_lines = REOPEN_STDIN;
+#endif
         }
         readpos = 0;
         readeof = 0;
@@ -1026,9 +1038,6 @@ static void reinitialize(void)
         max_fline = -1;
         cur_fline = 0;
         max_lineno = 0;
-#if ENABLE_FEATURE_LESS_FLAGS
-        num_lines = filename ? READING_FILE : READING_STDIN;
-#endif
         open_file_and_read_lines();
 #if ENABLE_FEATURE_LESS_ASK_TERMINAL
         if (G.winsize_err)