[PATCH] dmd: Allow storing early logs before writing to disk

[David Michael]

* modules/dmd.scm (main): Start logging to a buffer instead of a
  file when the logfile option is set to "delayed".
* modules/dmd/comm.scm (start-logging-to-buffer): New procedure.
  (start-logging): If logs were being written to a string port,
  write its contents to the log file.
---

Hi,

When using dmd to bring up a read-only file system, it will quit when it
fails to open a log file for writing.

This is a proof-of-concept patch that adds the option to start writing
logs to a string port.  It allows having a dmdconf.scm that runs fsck,
makes the disk writable, and then starts writing past and future log
messages to disk with (start-logging "/var/log/dmd.log").

Does anyone have any thoughts on this?  Is there a better way to handle
this case?

Thanks.

David

 modules/dmd.scm      |  7 +++++--
 modules/dmd/comm.scm | 17 ++++++++++++++---
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/modules/dmd.scm b/modules/dmd.scm
index cf72d7a..e0f69c7 100644
--- a/modules/dmd.scm
+++ b/modules/dmd.scm
@@ -97,7 +97,8 @@
                  (make <option>
                    #:long "logfile" #:short #\l
                    #:takes-arg? #t #:optional-arg? #f #:arg-name "FILE"
-                   #:description "log actions in FILE"
+                   #:description
+                   "log actions in FILE or to a buffer if FILE is \"delayed\""
                    #:action (lambda (file)
                               (set! logfile file)))
                  (make <option>
@@ -137,7 +138,9 @@
     (and socket-file
         (verify-dir (dirname socket-file) insecure))
     ;; Enable logging as first action.
-    (start-logging logfile)
+    (if (string-ci=? logfile "delayed")
+      (start-logging-to-buffer)
+      (start-logging logfile))
 
     ;; Send output to log and clients.
     (set-current-output-port dmd-output-port)
diff --git a/modules/dmd/comm.scm b/modules/dmd/comm.scm
index fb08629..aeb45ca 100644
--- a/modules/dmd/comm.scm
+++ b/modules/dmd/comm.scm
@@ -37,6 +37,7 @@
             read-command
 
             start-logging
+            start-logging-to-buffer
             stop-logging
             %current-client-socket
             dmd-output-port))
@@ -103,10 +104,20 @@ return the socket."
 ;; Port for logging.  This must always be a valid port, never `#f'.
 (define log-output-port (%make-void-port "w"))
 (define (start-logging file)
-  (let ((directory (dirname file)))
+  (let ((directory (dirname file)) (oldport log-output-port))
     (unless (file-exists? directory)
-      (mkdir directory)))
-  (set! log-output-port (open-file file "al")))   ; line-buffered port
+      (mkdir directory))
+    (set! log-output-port (open-file file "al"))  ; line-buffered port
+    ;; Attempt to dump any buffered log data to the given log file.  This only
+    ;; succeeds if log-output-port was an open output string port, as verified
+    ;; by get-output-string.  Otherwise, logging to a file is started normally.
+    (catch #t
+      (lambda ()
+        (display (get-output-string oldport) log-output-port)
+        (close-output-port oldport))
+      noop)))
+(define (start-logging-to-buffer)
+  (set! log-output-port (open-output-string)))
 (define (stop-logging)
   (close-port log-output-port)
   (set! log-output-port (%make-void-port "w")))
-- 
1.9.3