svlogd: blocking on ENOSPC

[Gerrit Pape <pape@smarden.org>]

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Hi, svlogd, just as multilog, sleeps and retries in case it's unable to
write to the current logfile in a log directory and the system is ``out
of disk space''.  This usually makes the service block because svlogd
stops reading from the pipe.  Even though the space for logs can be
calculated properly, if a log partition fills up by accident, it can
bring the system in a troublesome state.

Here's a patch that makes svlogd remove the oldest of rotated log files
in the log directory in case the disk is full.  In the worst case only
the current logfile will be left.  I would be interested in your
opinions.

Regards, Gerrit.

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diff -u -r1.7 -r1.8
--- src/svlogd.c	7 Oct 2004 07:56:29 -0000	1.7
+++ src/svlogd.c	7 Oct 2004 14:40:56 -0000	1.8
@@ -287,8 +287,41 @@
     if (len > ((dir +n)->sizemax -(dir +n)->size))
       len =(dir +n)->sizemax -(dir +n)->size;
   }
-  while ((i =write((dir +n)->fdcur, s, len)) == -1)
+  while ((i =write((dir +n)->fdcur, s, len)) == -1) {
+    if (errno == ENOSPC) {
+      DIR *d;
+      direntry *f;
+      char oldest[FMT_PTIME];
+
+      while (fchdir((dir +n)->fddir) == -1)
+        pause2("unable to change directory, want remove old logfile",
+               (dir +n)->name);
+      oldest[0] ='A'; oldest[1] =oldest[27] =0;
+      while (! (d =opendir(".")))
+        pause2("unable to open directory, want remove old logfile",
+               (dir +n)->name);
+      errno =0;
+      while ((f =readdir(d)))
+        if ((f->d_name[0] == '@') && (str_len(f->d_name) == 27))
+          if (str_diff(f->d_name, oldest) < 0) byte_copy(oldest, 27, f->d_name);
+      if (errno) warn2("unable to read directory, want remove old logfile",
+                       (dir +n)->name);
+      closedir(d);
+      if (*oldest == '@') {
+        strerr_warn5(WARNING, "out of disk space, delete: ", (dir +n)->name,
+                     "/", oldest, 0);
+        if (unlink(oldest) == -1)
+          warn2("unable to unlink oldest logfile", (dir +n)->name);
+        else
+          i =1;
+      }
+      while (fchdir(fdwdir) == -1)
+        pause1("unable to change to initial working directory");
+      if (i) continue;
+    }
     pause2("unable to write to current", (dir +n)->name);
+  }
+
   (dir +n)->size +=i;
   if ((dir +n)->sizemax)
     if (s[i -1] == '\n')