less: improve regular file detection in line counting code

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

diff --git a/miscutils/less.c b/miscutils/less.c
index b38fcf76625c7fff16c53f312a964660f6b493d8..be8d20e66a1120648e55d5ac7b2b0376d27aedab 100644 (file)
--- 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)