tail: implement -F

function                                             old     new   delta
tail_main                                           1190    1494    +304

Signed-off-by: Eric Lammerts <busybox@lists.lammerts.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 66 insertions, 21 deletions

diff --git a/coreutils/Config.in b/coreutils/Config.in
index 1bc047c9a..cacfb9661 100644
--- a/coreutils/Config.in
+++ b/coreutils/Config.in
@@ -635,7 +635,7 @@ config TAIL
           from files.
 
 config FEATURE_FANCY_TAIL
-        bool "Enable extra tail options (-q, -s, and -v)"
+        bool "Enable extra tail options (-q, -s, -v, and -F)"
         default y
         depends on TAIL
         help
diff --git a/coreutils/tail.c b/coreutils/tail.c
index 3ce6be0bd..ef1326c83 100644
--- a/coreutils/tail.c
+++ b/coreutils/tail.c
@@ -85,18 +85,15 @@ int tail_main(int argc, char **argv)
         unsigned count = 10;
         unsigned sleep_period = 1;
         bool from_top;
-        int header_threshhold = 1;
         const char *str_c, *str_n;
 
         char *tailbuf;
         size_t tailbufsize;
-        int taillen = 0;
-        int newlines_seen = 0;
-        int nfiles, nread, nwrite, i, opt;
-        unsigned seen;
+        unsigned header_threshhold = 1;
+        unsigned nfiles;
+        int i, opt;
 
         int *fds;
-        char *s, *buf;
         const char *fmt;
 
 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
@@ -110,8 +107,9 @@ int tail_main(int argc, char **argv)
         }
 #endif
 
-        IF_FEATURE_FANCY_TAIL(opt_complementary = "s+";) /* -s N */
-        opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:v"),
+        /* -s NUM, -F imlies -f */
+        IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
+        opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 #define FOLLOW (opt & 0x1)
 #define COUNT_BYTES (opt & 0x2)
@@ -119,8 +117,12 @@ int tail_main(int argc, char **argv)
         if (opt & 0x2) count = eat_num(str_c); // -c
         if (opt & 0x4) count = eat_num(str_n); // -n
 #if ENABLE_FEATURE_FANCY_TAIL
-        if (opt & 0x8) header_threshhold = INT_MAX; // -q
+        /* q: make it impossible for nfiles to be > header_threshhold */
+        if (opt & 0x8) header_threshhold = UINT_MAX; // -q
         if (opt & 0x20) header_threshhold = 0; // -v
+#define FOLLOW_RETRY (opt & 0x40)
+#else
+#define FOLLOW_RETRY 0
 #endif
         argc -= optind;
         argv += optind;
@@ -128,19 +130,21 @@ int tail_main(int argc, char **argv)
         G.status = EXIT_SUCCESS;
 
         /* open all the files */
-        fds = xmalloc(sizeof(int) * (argc + 1));
+        fds = xmalloc(sizeof(fds[0]) * (argc + 1));
         if (!argv[0]) {
                 struct stat statbuf;
 
-                if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
+                if (fstat(STDIN_FILENO, &statbuf) == 0
+                 && S_ISFIFO(statbuf.st_mode)
+                ) {
                         opt &= ~1; /* clear FOLLOW */
                 }
-                *argv = (char *) bb_msg_standard_input;
+                argv[0] = (char *) bb_msg_standard_input;
         }
         nfiles = i = 0;
         do {
                 int fd = open_or_warn_stdin(argv[i]);
-                if (fd < 0) {
+                if (fd < 0 && !FOLLOW_RETRY) {
                         G.status = EXIT_FAILURE;
                         continue;
                 }
@@ -161,9 +165,18 @@ int tail_main(int argc, char **argv)
         tailbuf = xmalloc(tailbufsize);
 
         /* tail the files */
-        fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
+        fmt = header_fmt + 1; /* skip header leading newline on first output */
         i = 0;
         do {
+                char *buf;
+                int taillen;
+                int newlines_seen;
+                unsigned seen;
+                int nread;
+
+                if (ENABLE_FEATURE_FANCY_TAIL && fds[i] < 0)
+                        continue; /* may happen with -E */
+
                 if (nfiles > header_threshhold) {
                         tail_xprint_header(fmt, argv[i]);
                         fmt = header_fmt;
@@ -192,13 +205,13 @@ int tail_main(int argc, char **argv)
                 newlines_seen = 0;
                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
                         if (from_top) {
-                                nwrite = nread;
+                                int nwrite = nread;
                                 if (seen < count) {
                                         if (COUNT_BYTES) {
                                                 nwrite -= (count - seen);
                                                 seen = count;
                                         } else {
-                                                s = buf;
+                                                char *s = buf;
                                                 do {
                                                         --nwrite;
                                                         if (*s++ == '\n' && ++seen == count) {
@@ -231,6 +244,7 @@ int tail_main(int argc, char **argv)
                                                 taillen += nread;
                                         } else {
                                                 int extra = (buf[nread-1] != '\n');
+                                                char *s;
 
                                                 k = newlines_seen + newlines_in_buf + extra - count;
                                                 s = tailbuf;
@@ -257,23 +271,54 @@ int tail_main(int argc, char **argv)
                 }
         } while (++i < nfiles);
 
-        buf = xrealloc(tailbuf, BUFSIZ);
+        tailbuf = xrealloc(tailbuf, BUFSIZ);
 
         fmt = NULL;
 
         if (FOLLOW) while (1) {
                 sleep(sleep_period);
+
                 i = 0;
                 do {
+                        int nread;
+                        const char *filename = argv[i];
+                        int fd = fds[i];
+
+                        if (FOLLOW_RETRY) {
+                                struct stat sbuf, fsbuf;
+
+                                if (fd < 0
+                                 || fstat(fd, &fsbuf) < 0
+                                 || stat(filename, &sbuf) < 0
+                                 || fsbuf.st_dev != sbuf.st_dev
+                                 || fsbuf.st_ino != sbuf.st_ino
+                                ) {
+                                        int new_fd;
+
+                                        if (fd >= 0)
+                                                close(fd);
+                                        new_fd = open(filename, O_RDONLY);
+                                        if (new_fd >= 0) {
+                                                bb_error_msg("%s has %s; following end of new file",
+                                                        filename, (fd < 0) ? "appeared" : "been replaced"
+                                                );
+                                        } else if (fd >= 0) {
+                                                bb_perror_msg("%s has become inaccessible", filename);
+                                        }
+                                        fds[i] = fd = new_fd;
+                                }
+                        }
+                        if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
+                                continue;
                         if (nfiles > header_threshhold) {
                                 fmt = header_fmt;
                         }
-                        while ((nread = tail_read(fds[i], buf, BUFSIZ)) > 0) {
+                        while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
                                 if (fmt) {
-                                        tail_xprint_header(fmt, argv[i]);
+                                        tail_xprint_header(fmt, filename);
                                         fmt = NULL;
                                 }
-                                xwrite(STDOUT_FILENO, buf, nread);
+                                xwrite(STDOUT_FILENO, tailbuf, nread);
                         }
                 } while (++i < nfiles);
         }