New APIs: compress-out, compress-device-out.

These APIs let you copy compressed files or devices out from the disk
image.

Compression is useful for large images which are mostly zeroes.  We
cannot currently do sparseness detection, and compression gives us a
form of zero detection for free.

Example usage:

$ guestfish --ro -a /dev/vg_pin/F16x64 -i \
    compress-out gzip /etc/passwd /tmp/passwd.gz
$ file -z /tmp/passwd.gz
/tmp/passwd.gz: ASCII text (gzip compressed data, was "passwd", from
Unix, last modified: Sun Aug 28 14:40:46 2011)

1 files changed, 207 insertions, 0 deletions

diff --git a/daemon/compress.c b/daemon/compress.c
new file mode 100644
index 00000000..d08d3cc9
--- /dev/null
+++ b/daemon/compress.c
@@ -0,0 +1,207 @@
+/* libguestfs - the guestfsd daemon
+ * Copyright (C) 2011 Red Hat Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+
+#include "guestfs_protocol.h"
+#include "daemon.h"
+#include "actions.h"
+
+/* Has one FileOut parameter. */
+static int
+do_compressX_out (const char *file, const char *filter, int is_device)
+{
+  int r;
+  FILE *fp;
+  char *cmd;
+  char buf[GUESTFS_MAX_CHUNK_SIZE];
+
+  /* The command will look something like:
+   *   gzip -c /sysroot%s     # file
+   * or:
+   *   gzip -c < %s           # device
+   *
+   * We have to quote the file or device name.
+   *
+   * The unnecessary redirect for devices is there because lzop
+   * unhelpfully refuses to compress anything that isn't a regular
+   * file.
+   */
+  if (!is_device) {
+    if (asprintf_nowarn (&cmd, "%s %R", filter, file) == -1) {
+      reply_with_perror ("asprintf");
+      return -1;
+    }
+  } else {
+    if (asprintf_nowarn (&cmd, "%s < %Q", filter, file) == -1) {
+      reply_with_perror ("asprintf");
+      return -1;
+    }
+  }
+
+  if (verbose)
+    fprintf (stderr, "%s\n", cmd);
+
+  fp = popen (cmd, "r");
+  if (fp == NULL) {
+    reply_with_perror ("%s", cmd);
+    free (cmd);
+    return -1;
+  }
+  free (cmd);
+
+  /* Now we must send the reply message, before the file contents.  After
+   * this there is no opportunity in the protocol to send any error
+   * message back.  Instead we can only cancel the transfer.
+   */
+  reply (NULL, NULL);
+
+  while ((r = fread (buf, 1, sizeof buf, fp)) > 0) {
+    if (send_file_write (buf, r) < 0) {
+      pclose (fp);
+      return -1;
+    }
+  }
+
+  if (ferror (fp)) {
+    perror (file);
+    send_file_end (1);		/* Cancel. */
+    pclose (fp);
+    return -1;
+  }
+
+  if (pclose (fp) != 0) {
+    perror (file);
+    send_file_end (1);		/* Cancel. */
+    return -1;
+  }
+
+  if (send_file_end (0))	/* Normal end of file. */
+    return -1;
+
+  return 0;
+}
+
+#define CHECK_SUPPORTED(prog)                                           \
+  if (!prog_exists (prog)) {                                            \
+    /* note: substring "not supported" must appear in this error */     \
+    reply_with_error ("compression type %s is not supported", prog);    \
+    return -1;                                                          \
+  }
+
+static int
+get_filter (const char *ctype, int level, char *ret, size_t n)
+{
+  if (STREQ (ctype, "compress")) {
+    CHECK_SUPPORTED ("compress");
+    if (level != -1) {
+      reply_with_error ("compress: cannot use optional level parameter with this compression type");
+      return -1;
+    }
+    snprintf (ret, n, "compress -c");
+    return 0;
+  }
+  else if (STREQ (ctype, "gzip")) {
+    CHECK_SUPPORTED ("gzip");
+    if (level == -1)
+      snprintf (ret, n, "gzip -c");
+    else if (level >= 1 && level <= 9)
+      snprintf (ret, n, "gzip -c -%d", level);
+    else {
+      reply_with_error ("gzip: incorrect value for level parameter");
+      return -1;
+    }
+    return 0;
+  }
+  else if (STREQ (ctype, "bzip2")) {
+    CHECK_SUPPORTED ("bzip2");
+    if (level == -1)
+      snprintf (ret, n, "bzip2 -c");
+    else if (level >= 1 && level <= 9)
+      snprintf (ret, n, "bzip2 -c -%d", level);
+    else {
+      reply_with_error ("bzip2: incorrect value for level parameter");
+      return -1;
+    }
+    return 0;
+  }
+  else if (STREQ (ctype, "xz")) {
+    CHECK_SUPPORTED ("xz");
+    if (level == -1)
+      snprintf (ret, n, "xz -c");
+    else if (level >= 0 && level <= 9)
+      snprintf (ret, n, "xz -c -%d", level);
+    else {
+      reply_with_error ("xz: incorrect value for level parameter");
+      return -1;
+    }
+    return 0;
+  }
+  else if (STREQ (ctype, "lzop")) {
+    CHECK_SUPPORTED ("lzop");
+    if (level == -1)
+      snprintf (ret, n, "lzop -c");
+    else if (level >= 1 && level <= 9)
+      snprintf (ret, n, "lzop -c -%d", level);
+    else {
+      reply_with_error ("lzop: incorrect value for level parameter");
+      return -1;
+    }
+    return 0;
+  }
+
+  reply_with_error ("unknown compression type");
+  return -1;
+}
+
+/* Has one FileOut parameter. */
+/* Takes optional arguments, consult optargs_bitmask. */
+int
+do_compress_out (const char *ctype, const char *file, int level)
+{
+  char filter[64];
+
+  if (!(optargs_bitmask & GUESTFS_COMPRESS_OUT_LEVEL_BITMASK))
+    level = -1;
+
+  if (get_filter (ctype, level, filter, sizeof filter) == -1)
+    return -1;
+
+  return do_compressX_out (file, filter, 0);
+}
+
+/* Has one FileOut parameter. */
+/* Takes optional arguments, consult optargs_bitmask. */
+int
+do_compress_device_out (const char *ctype, const char *file, int level)
+{
+  char filter[64];
+
+  if (!(optargs_bitmask & GUESTFS_COMPRESS_DEVICE_OUT_LEVEL_BITMASK))
+    level = -1;
+
+  if (get_filter (ctype, level, filter, sizeof filter) == -1)
+    return -1;
+
+  return do_compressX_out (file, filter, 1);
+}