Initial support for filtering TAR files through an external program.

At the moment this is hard-coded to pipe data through "bzip2 -c", but
this should be made flexible later.

diff --git a/store.cc b/store.cc
index 70be126..26797b3 100644 (file)
--- a/store.cc
+++ b/store.cc
@@ -10,6 +10,8 @@
 #include <stdio.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/resource.h>
+#include <sys/wait.h>
 #include <unistd.h>
 #include <fcntl.h>
 #include <time.h>
@@ -26,21 +28,96 @@ using std::list;
 using std::set;
 using std::string;
 
+static char *const filter_program[] = {"bzip2", "-c", NULL};
+
+static void cloexec(int fd)
+{
+    long flags = fcntl(fd, F_GETFD);
+
+    if (flags < 0)
+        return;
+
+    fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
+}
+
 Tarfile::Tarfile(const string &path, const string &segment)
     : size(0),
       segment_name(segment)
 {
-    if (tar_open(&t, (char *)path.c_str(), NULL, O_WRONLY | O_CREAT, 0600,
-                 TAR_VERBOSE | TAR_GNU) == -1)
+    real_fd = open(path.c_str(), O_WRONLY | O_CREAT, 0600);
+    if (real_fd < 0)
+        throw IOException("Error opening output file");
+
+    filter_fd = spawn_filter(real_fd);
+
+    if (tar_fdopen(&t, filter_fd, (char *)path.c_str(), NULL,
+                   O_WRONLY | O_CREAT, 0600, TAR_VERBOSE | TAR_GNU) == -1)
         throw IOException("Error opening Tarfile");
 }
 
 Tarfile::~Tarfile()
 {
+    /* Close the tar file... */
     tar_append_eof(t);
 
     if (tar_close(t) != 0)
         throw IOException("Error closing Tarfile");
+
+    /* ...and wait for filter process to finish. */
+    int status;
+    waitpid(filter_pid, &status, 0);
+
+    if (!WIFEXITED(status) || WEXITSTATUS(status) != 0) {
+        throw IOException("Filter process error");
+    }
+
+    close(real_fd);
+}
+
+/* Launch a child process which can act as a filter (compress, encrypt, etc.)
+ * on the TAR output.  The file descriptor to which output should be written
+ * must be specified; the return value is the file descriptor which will be
+ * attached to the standard input of the filter program. */
+int Tarfile::spawn_filter(int fd_out)
+{
+    int fds[2];
+
+    /* Create a pipe for communicating with the filter process. */
+    if (pipe(fds) < 0) {
+        throw IOException("Unable to create pipe for filter");
+    }
+
+    /* Create a child process which can exec() the filter program. */
+    filter_pid = fork();
+    if (filter_pid < 0)
+        throw IOException("Unable to fork filter process");
+
+    if (filter_pid > 0) {
+        /* Parent process */
+        close(fds[0]);
+        cloexec(fds[1]);
+    } else {
+        /* Child process.  Rearrange file descriptors.  stdin is fds[0], stdout
+         * is fd_out, stderr is unchanged. */
+        close(fds[1]);
+
+        if (dup2(fds[0], 0) < 0)
+            exit(1);
+        close(fds[0]);
+
+        if (dup2(fd_out, 1) < 0)
+            exit(1);
+        close(fd_out);
+
+        /* Exec the filter program. */
+        execvp(filter_program[0], filter_program);
+
+        /* Should not reach here except for error cases. */
+        fprintf(stderr, "Could not exec filter: %m\n");
+        exit(1);
+    }
+
+    return fds[1];
 }
 
 void Tarfile::write_object(int id, const char *data, size_t len)
@@ -91,6 +168,23 @@ void Tarfile::internal_write_object(const string &path,
     size += blocks * T_BLOCKSIZE;
 }
 
+/* Estimate the size based on the size of the actual output file on disk.
+ * However, the filter may not have written all data yet, and in the event that
+ * it is buffering data to a large extent, also use */
+size_t Tarfile::size_estimate()
+{
+    struct stat statbuf;
+
+    if (fstat(real_fd, &statbuf) == 0) {
+        size_t disk_size = statbuf.st_size;
+
+        if (disk_size >= size / 128)
+            return disk_size;
+    }
+
+    return size;
+}
+
 static const size_t SEGMENT_SIZE = 4 * 1024 * 1024;
 
 ObjectReference TarSegmentStore::write_object(const char *data, size_t len,
@@ -105,7 +199,7 @@ ObjectReference TarSegmentStore::write_object(const char *data, size_t len,
 
         segment->name = generate_uuid();
 
-        string filename = path + "/" + segment->name + ".tar";
+        string filename = path + "/" + segment->name + ".tar.bz2";
         segment->file = new Tarfile(filename, segment->name);
 
         segment->count = 0;

diff --git a/store.h b/store.h
index 1ef5db4..aa96160 100644 (file)
--- a/store.h
+++ b/store.h
@@ -49,10 +49,11 @@ public:
     Tarfile(const std::string &path, const std::string &segment);
     ~Tarfile();
 
+    int spawn_filter(int fd_out);
     void write_object(int id, const char *data, size_t len);
 
     // Return an estimate of the size of the file.
-    size_t size_estimate() { return size; }
+    size_t size_estimate();
 
     void internal_write_object(const std::string &path,
                                const char *data, size_t len);
@@ -61,6 +62,10 @@ private:
     size_t size;
     std::string segment_name;
     TAR *t;
+
+    /* Filter support. */
+    int real_fd, filter_fd;
+    pid_t filter_pid;
 };
 
 class TarSegmentStore {