New options for tail: --follow=name, --follow=descriptor, --allow-missing

(Follow_mode): New enum.
(n_live_files): New function.
(tail_forever): Avoid starvation with --follow=name and a
continually-growing unlinked or renamed file.

1 files changed, 124 insertions, 46 deletions

diff --git a/src/tail.c b/src/tail.c
index 5d797dc9c..fe90e3672 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -31,6 +31,7 @@
 #include <sys/types.h>
 
 #include "system.h"
+#include "argmatch.h"
 #include "xstrtoul.h"
 #include "error.h"
 #include "safe-read.h"
@@ -51,13 +52,30 @@
 # define BUFSIZ (512 * 8)
 #endif
 
+/* FIXME: make Follow_name the default?  */
+#define DEFAULT_FOLLOW_MODE Follow_descriptor
+
 enum Follow_mode
 {
-  /* FIXME: describe */
-  follow_name,
+  /* Follow the name of each file: if the file is renamed, try to reopen
+     that name and track the end of the new file if/when it's recreated.
+     This is useful for tracking logs that are occasionally rotated.  */
+  Follow_name = 1,
+
+  /* Follow each descriptor obtained upon opening a file.
+     That means we'll continue to follow the end of a file even after
+     it has been renamed or unlinked.  */
+  Follow_descriptor = 2,
+};
 
-  /* FIXME: describe */
-  follow_descriptor,
+static char const *const follow_mode_string[] =
+{
+  "descriptor", "name", 0
+};
+
+static enum Follow_mode const follow_mode_map[] =
+{
+  Follow_descriptor, Follow_name,
 };
 
 struct File_spec
@@ -82,6 +100,9 @@ struct File_spec
   unsigned int n_unchanged_stats;
 
   /* FIXME: describe */
+  unsigned int n_consecutive_size_changes;
+
+  /* FIXME: describe */
   int missing;
 };
 
@@ -94,8 +115,7 @@ static int count_lines;
 
 /* Whether we follow the name of each file or the file descriptor
    that is initially associated with each name.  */
-/* FIXME: make follow_name the default? */
-static enum Follow_mode follow_mode;
+static enum Follow_mode follow_mode = Follow_descriptor;
 
 /* If nonzero, read from the ends of all specified files until killed.  */
 static int forever;
@@ -113,7 +133,10 @@ enum header_mode
 };
 
 /* FIXME: describe -- add option */
-static unsigned long max_n_unchanged_stats = 5;
+static unsigned long max_n_unchanged_stats_between_opens = 5;
+
+/* FIXME: describe -- add option */
+static unsigned long max_n_consecutive_size_changes = 200;
 
 /* The name this program was run with.  */
 char *program_name;
@@ -132,11 +155,9 @@ static int show_version;
 
 static struct option const long_options[] =
 {
-  {"allow-missing", required_argument, NULL, CHAR_MAX + 1},
+  {"allow-missing", no_argument, NULL, CHAR_MAX + 1},
   {"bytes", required_argument, NULL, 'c'},
-  {"follow", no_argument, NULL, 'f'},
-  {"follow-descriptor", no_argument, NULL, CHAR_MAX + 2},
-  {"follow-name", no_argument, NULL, CHAR_MAX + 3},
+  {"follow", optional_argument, NULL, 'f'},
   {"lines", required_argument, NULL, 'n'},
   {"quiet", no_argument, NULL, 'q'},
   {"silent", no_argument, NULL, 'q'},
@@ -164,8 +185,9 @@ Print last 10 lines of each FILE to standard output.\n\
 With more than one FILE, precede each with a header giving the file name.\n\
 With no FILE, or when FILE is -, read standard input.\n\
 \n\
+      --allow-missing      FIXME\n\
   -c, --bytes=N            output the last N bytes\n\
-  -f, --follow             output appended data as the file grows\n\
+  -f, --follow[={name|descriptor}] output appended data as the file grows\n\
   -n, --lines=N            output the last N lines, instead of last 10\n\
   -q, --quiet, --silent    never output headers giving file names\n\
   -s, --sleep-interval=S   with -f, sleep S seconds between iterations\n\
@@ -180,6 +202,7 @@ b for 512, k for 1024, m for 1048576 (1 Meg).  A first OPTION of -VALUE\n\
 or +VALUE is treated like -n VALUE or -n +VALUE unless VALUE has one of\n\
 the [bkm] suffix multipliers, in which case it is treated like -c VALUE\n\
 or -c +VALUE.\n\
+FIXME: describe name vs descriptor\n\
 "));
       puts (_("\nReport bugs to <bug-textutils@gnu.org>."));
     }
@@ -563,7 +586,7 @@ start_lines (const char *pretty_filename, int fd, long int n_lines)
   return 0;
 }
 
-/* Display file FILENAME from the current position in FD to the end.
+/* Display file PRETTY_FILENAME from the current position in FD to the end.
    Return the number of bytes read from the file.  */
 
 static long
@@ -593,12 +616,12 @@ dump_remainder (const char *pretty_filename, int fd)
 static void
 recheck (struct File_spec *f)
 {
-  /* open/fstat the file and announce if dev/ino
-     have changed */
+  /* open/fstat the file and announce if dev/ino have changed */
   struct stat new_stats;
   int fd;
   int fail = 0;
   int is_stdin = (STREQ (f->name, "-"));
+  int was_missing = f->missing;
 
   fd = (is_stdin ? STDIN_FILENO : open (f->name, O_RDONLY));
 
@@ -609,14 +632,26 @@ recheck (struct File_spec *f)
   if (fd == -1 || fstat (fd, &new_stats) < 0)
     {
       fail = 1;
-      error (0, errno, "%s", pretty_name (f));
+      if (f->missing)
+	{
+	  if (!was_missing)
+	    error (0, 0, "`%s' has been removed", pretty_name (f));
+	  else
+	    {
+	      /* say nothing... it's still missing */
+	    }
+	}
+      else
+	{
+	  error (0, errno, "%s", pretty_name (f));
+	}
     }
   else if (!S_ISREG (new_stats.st_mode)
 	   && !S_ISFIFO (new_stats.st_mode))
     {
       fail = 1;
       error (0, 0,
-	     _("%s has been replaced with a non-regular file;  \
+	     _("`%s' has been replaced with a non-regular file;  \
 cannot follow end of non-regular file"),
 	     pretty_name (f));
     }
@@ -629,26 +664,36 @@ cannot follow end of non-regular file"),
     }
   else if (f->ino != new_stats.st_ino || f->dev != new_stats.st_dev)
     {
-      /* Close the old one.  */
-      close_fd (f->fd, pretty_name (f));
+      if (f->fd == -1)
+	{
+	  error (0, 0,
+		 _("`%s' has appeared;  following end of new file"),
+		 pretty_name (f));
+	}
+      else
+	{
+	  /* Close the old one.  */
+	  close_fd (f->fd, pretty_name (f));
 
-      /* File has been replaced (e.g., via log rotation) --
-         tail the new one.  */
-      error (0, 0,
-	     _("%s has been replaced;  following end of new file"),
-	     pretty_name (f));
+	  /* File has been replaced (e.g., via log rotation) --
+	     tail the new one.  */
+	  error (0, 0,
+		 _("`%s' has been replaced;  following end of new file"),
+		 pretty_name (f));
+	}
 
       f->fd = fd;
       f->size = new_stats.st_size;
       f->dev = new_stats.st_dev;
       f->ino = new_stats.st_ino;
       f->n_unchanged_stats = 0;
+      f->n_consecutive_size_changes = 0;
       /* FIXME: check lseek return value  */
       lseek (f->fd, new_stats.st_size, SEEK_SET);
     }
   else if (f->missing)
     {
-      error (0, 0, _("%s has reappeared"), pretty_name (f));
+      error (0, 0, _("`%s' has reappeared"), pretty_name (f));
       f->missing = 0;
 
       f->fd = fd;
@@ -656,6 +701,7 @@ cannot follow end of non-regular file"),
       f->dev = new_stats.st_dev;
       f->ino = new_stats.st_ino;
       f->n_unchanged_stats = 0;
+      f->n_consecutive_size_changes = 0;
       /* FIXME: check lseek return value  */
       lseek (f->fd, new_stats.st_size, SEEK_SET);
     }
@@ -665,6 +711,22 @@ cannot follow end of non-regular file"),
     }
 }
 
+/* FIXME: describe */
+
+static unsigned int
+n_live_files (const struct File_spec *f, int n_files)
+{
+  int i;
+  unsigned int n_live = 0;
+
+  for (i = 0; i < n_files; i++)
+    {
+      if (f[i].fd >= 0)
+	++n_live;
+    }
+  return n_live;
+}
+
 /* Tail NFILES files forever, or until killed.
    The pertinent information for each file is stored in an entry of F.
    Loop over each of them, doing an fstat to see if they have changed size,
@@ -683,18 +745,18 @@ tail_forever (struct File_spec *f, int nfiles)
     {
       int i;
       int any_changed;
-      int any_live_files;
 
-      any_live_files = 0;
       any_changed = 0;
       for (i = 0; i < nfiles; i++)
 	{
 	  struct stat stats;
 
-	  if (f[i].fd < 0 && !f[i].missing)
-	    continue;
-
-	  any_live_files = 1;
+	  if (f[i].fd < 0)
+	    {
+	      if (f[i].missing)
+		recheck (&f[i]);
+	      continue;
+	    }
 
 	  if (fstat (f[i].fd, &stats) < 0)
 	    {
@@ -705,8 +767,9 @@ tail_forever (struct File_spec *f, int nfiles)
 
 	  if (stats.st_size == f[i].size)
 	    {
-	      if (++f[i].n_unchanged_stats > max_n_unchanged_stats
-		  && follow_mode == follow_name)
+	      f[i].n_consecutive_size_changes = 0;
+	      if (++f[i].n_unchanged_stats > max_n_unchanged_stats_between_opens
+		  && follow_mode == Follow_name)
 		{
 		  recheck (&f[i]);
 		  f[i].n_unchanged_stats = 0;
@@ -715,9 +778,18 @@ tail_forever (struct File_spec *f, int nfiles)
 	      continue;
 	    }
 
-	  /* FIXME-now:
-	     Otherwise, a file that's unlinked or moved aside, yet always
-	     growing will never be recognized has having been renamed.  */
+	  /* Size changed.  */
+	  ++f[i].n_consecutive_size_changes;
+
+	  /* Ensure that a file that's unlinked or moved aside, yet always
+	     growing will be recognized has having been renamed.  */
+	  if (follow_mode == Follow_name
+	      && (f[i].n_consecutive_size_changes
+		  > max_n_consecutive_size_changes))
+	    {
+	      f[i].n_consecutive_size_changes = 0;
+	      recheck (&f[i]);
+	    }
 
 	  /* This file has changed size.  Print out what we can, and
 	     then keep looping.  */
@@ -746,7 +818,7 @@ tail_forever (struct File_spec *f, int nfiles)
 	  f[i].size += dump_remainder (pretty_name (&f[i]), f[i].fd);
 	}
 
-      if (!any_live_files /* FIXME-now: && ! allow_missing */ )
+      if (n_live_files (f, nfiles) == 0 && ! allow_missing)
 	{
 	  error (0, 0, _("no files remaining"));
 	  break;
@@ -951,6 +1023,7 @@ tail_file (struct File_spec *f, off_t n_units)
 	      f->dev = stats.st_dev;
 	      f->ino = stats.st_ino;
 	      f->n_unchanged_stats = 0;
+	      f->n_consecutive_size_changes = 0;
 	    }
 	}
       else
@@ -1127,7 +1200,8 @@ parse_options (int argc, char **argv,
   count_lines = 1;
   forever = from_start = print_headers = 0;
 
-  while ((c = getopt_long (argc, argv, "c:n:fqs:v", long_options, NULL)) != -1)
+  while ((c = getopt_long (argc, argv, "c:n:f::qs:v", long_options, NULL))
+	 != -1)
     {
       switch (c)
 	{
@@ -1166,20 +1240,24 @@ parse_options (int argc, char **argv,
 
 	case 'f':
 	  forever = 1;
+	  if (optarg == NULL)
+	    follow_mode = DEFAULT_FOLLOW_MODE;
+	  else
+	    {
+	      int i = argmatch (optarg, follow_mode_string);
+	      if (i < 0)
+		{
+		  invalid_arg (_("follow mode"), optarg, i);
+		  usage (1);
+		}
+	      follow_mode = follow_mode_map[i];
+	    }
 	  break;
 
 	case CHAR_MAX + 1:
 	  allow_missing = 1;
 	  break;
 
-	case CHAR_MAX + 2:
-	  follow_mode = follow_descriptor;
-	  break;
-
-	case CHAR_MAX + 3:
-	  follow_mode = follow_name;
-	  break;
-
 	case 'q':
 	  *header_mode = never;
 	  break;