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[Libguestfs] [PATCH] btrfs: Fix btrfs_subvolume_list on F18



The output of btrfs subvolume list has changed in F18 to include generation,
which breaks the parsing in btrfs_subvolume_list. This change replaces sscanf
with a more robust regular expression. The new regular expression should also
handle the addition of future unexpected columns.

Fixes RHBZ#903620
---
 daemon/Makefile.am |  6 +++--
 daemon/btrfs.c     | 67 ++++++++++++++++++++++++++++++++++++++++++------------
 2 files changed, 56 insertions(+), 17 deletions(-)

diff --git a/daemon/Makefile.am b/daemon/Makefile.am
index a05771e..1fe8e12 100644
--- a/daemon/Makefile.am
+++ b/daemon/Makefile.am
@@ -197,14 +197,16 @@ guestfsd_LDADD = \
 	$(LIBSOCKET) \
 	$(LIB_CLOCK_GETTIME) \
 	$(LIBINTL) \
-	$(SERVENT_LIB)
+	$(SERVENT_LIB) \
+  $(PCRE_LIBS)
 
 guestfsd_CPPFLAGS = -I$(top_srcdir)/gnulib/lib -I$(top_builddir)/gnulib/lib
 guestfsd_CFLAGS = \
 	$(WARN_CFLAGS) $(WERROR_CFLAGS) \
 	$(AUGEAS_CFLAGS) \
 	$(HIVEX_CFLAGS) \
-	$(YAJL_CFLAGS)
+	$(YAJL_CFLAGS) \
+  $(PCRE_CFLAGS)
 
 # Manual pages and HTML files for the website.
 man_MANS = guestfsd.8
diff --git a/daemon/btrfs.c b/daemon/btrfs.c
index 8ecde01..a940f0c 100644
--- a/daemon/btrfs.c
+++ b/daemon/btrfs.c
@@ -21,6 +21,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <inttypes.h>
+#include <pcre.h>
 #include <string.h>
 #include <unistd.h>
 
@@ -326,7 +327,7 @@ do_btrfs_subvolume_list (const char *fs)
   char *fs_buf;
   const char *argv[MAX_ARGS];
   size_t i = 0;
-  char *out, *err, **lines, *pos;
+  char *out, *err, **lines;
   size_t nr_subvolumes;
   int r;
 
@@ -358,13 +359,18 @@ do_btrfs_subvolume_list (const char *fs)
 
   /* Output is:
    *
-   * ID 256 top level 5 path test1
-   * ID 257 top level 5 path dir/test2
-   * ID 258 top level 5 path test3
+   * ID 256 gen 30 top level 5 path test1
+   * ID 257 gen 30 top level 5 path dir/test2
+   * ID 258 gen 30 top level 5 path test3
    *
-   * "ID <n>" is the subvolume ID.  "top level <n>" is the top level
-   * subvolume ID.  "path <str>" is the subvolume path, relative to
-   * the top of the filesystem.
+   * "ID <n>" is the subvolume ID.
+   * "gen <n>" is the generation when the root was created or last updated.
+   * "top level <n>" is the top level subvolume ID.
+   * "path <str>" is the subvolume path, relative to the top of the filesystem.
+   *
+   * Note that the order that each of the above is fixed, but different versions
+   * of btrfs may display different sets of data. Specifically, older versions
+   * of btrfs do not display gen.
    */
   nr_subvolumes = count_strings (lines);
 
@@ -384,33 +390,64 @@ do_btrfs_subvolume_list (const char *fs)
     return NULL;
   }
 
+  const char *errptr;
+  int erroffset;
+  pcre *re = pcre_compile ("ID\\s+(\\d+).*\\s"
+                           "top level\\s+(\\d+).*\\s"
+                           "path\\s(.*)",
+                           0, &errptr, &erroffset, NULL);
+  if (re == NULL) {
+    reply_with_error ("pcre_compile (%i): %s", erroffset, errptr);
+    free (ret->guestfs_int_btrfssubvolume_list_val);
+    free (ret);
+    free_stringslen (lines, nr_subvolumes);
+    return NULL;
+  }
+
   for (i = 0; i < nr_subvolumes; ++i) {
     /* To avoid allocations, reuse the 'line' buffer to store the
      * path.  Thus we don't need to free 'line', since it will be
      * freed by the calling (XDR) code.
      */
     char *line = lines[i];
+    #define N_MATCHES 3
+    int ovector[N_MATCHES * 3];
 
-    if (sscanf (line, "ID %" SCNu64 " top level %" SCNu64 " path ",
-                &ret->guestfs_int_btrfssubvolume_list_val[i].btrfssubvolume_id,
-                &ret->guestfs_int_btrfssubvolume_list_val[i].btrfssubvolume_top_level_id) != 2) {
+    if (pcre_exec (re, NULL, line, strlen(line), 0, 0,
+                   ovector, N_MATCHES * 3) < 0)
+    #undef N_MATCHES
+    {
     unexpected_output:
       reply_with_error ("unexpected output from 'btrfs subvolume list' command: %s", line);
       free_stringslen (lines, nr_subvolumes);
       free (ret->guestfs_int_btrfssubvolume_list_val);
       free (ret);
+      pcre_free(re);
       return NULL;
     }
 
-    pos = strstr (line, " path ");
-    if (pos == NULL)
-      goto unexpected_output;
-    pos += 6;
+    #if __WORDSIZE == 64
+      #define STRTOU64 strtoul
+    #else
+      #define STRTOU64 strtoull
+    #endif
+
+    errno = 0;
+    ret->guestfs_int_btrfssubvolume_list_val[i].btrfssubvolume_id =
+      STRTOU64(line + ovector[0], NULL, 10);
+    if (errno == ERANGE) goto unexpected_output;
+    ret->guestfs_int_btrfssubvolume_list_val[i].btrfssubvolume_top_level_id =
+      STRTOU64(line + ovector[2], NULL, 10);
+    if (errno == ERANGE) goto unexpected_output;
 
-    memmove (line, pos, strlen (pos) + 1);
+    #undef STRTOU64
+
+    memmove (line, line + ovector[4], ovector[5] + 1);
     ret->guestfs_int_btrfssubvolume_list_val[i].btrfssubvolume_path = line;
   }
 
+  pcre_free(re);
+
   return ret;
 }
 
-- 
1.8.1


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