Use /var/tmp for the cached appliance (for FHS compliance).

The FHS advises large files not to be stored in the root
filesystem[1], and that /var/tmp is persistent across reboots[2]
(whereas /tmp is possibly not[3]).

Therefore we should store the large cached supermin appliance in
/var/tmp instead of /tmp.  /tmp is still used for all other temporary
files and directories.

In either case you can override this by setting $TMPDIR.

[1] http://www.pathname.com/fhs/pub/fhs-2.3.html#THEROOTFILESYSTEM
[2] http://www.pathname.com/fhs/pub/fhs-2.3.html#VARTMPTEMPORARYFILESPRESERVEDBETWEE
[3] http://www.pathname.com/fhs/pub/fhs-2.3.html#TMPTEMPORARYFILES

5 files changed, 27 insertions, 6 deletions

diff --git a/fish/guestfish.pod b/fish/guestfish.pod
index 5ec6689e..0f318f04 100644
--- a/fish/guestfish.pod
+++ b/fish/guestfish.pod
@@ -1052,12 +1052,13 @@ set, it uses C<more>.
 
 =item TMPDIR
 
-Location of temporary directory, defaults to C</tmp>.
+Location of temporary directory, defaults to C</tmp> except for the
+cached supermin appliance which defaults to C</var/tmp>.
 
 If libguestfs was compiled to use the supermin appliance then the
 real appliance is cached in this directory, shared between all
 handles belonging to the same EUID.  You can use C<$TMPDIR> to
-configure another directory to use in case C</tmp> is not large
+configure another directory to use in case C</var/tmp> is not large
 enough.
 
 =back
diff --git a/src/appliance.c b/src/appliance.c
index 1b6b505e..ef724be5 100644
--- a/src/appliance.c
+++ b/src/appliance.c
@@ -308,7 +308,7 @@ check_for_cached_appliance (guestfs_h *g,
                             uid_t uid,
                             char **kernel, char **initrd, char **appliance)
 {
-  const char *tmpdir = guestfs_tmpdir ();
+  const char *tmpdir = guestfs___persistent_tmpdir ();
 
   /* len must be longer than the length of any pathname we can
    * generate in this function.
@@ -419,7 +419,7 @@ build_supermin_appliance (guestfs_h *g,
   if (g->verbose)
     guestfs___print_timestamped_message (g, "begin building supermin appliance");
 
-  const char *tmpdir = guestfs_tmpdir ();
+  const char *tmpdir = guestfs___persistent_tmpdir ();
 
   /* len must be longer than the length of any pathname we can
    * generate in this function.
diff --git a/src/guestfs-internal.h b/src/guestfs-internal.h
index 08b459bc..194c8928 100644
--- a/src/guestfs-internal.h
+++ b/src/guestfs-internal.h
@@ -257,6 +257,7 @@ extern char *guestfs_safe_strndup (guestfs_h *g, const char *str, size_t n);
 extern void *guestfs_safe_memdup (guestfs_h *g, void *ptr, size_t size);
 extern char *guestfs_safe_asprintf (guestfs_h *g, const char *fs, ...)
   __attribute__((format (printf,2,3)));
+extern const char *guestfs___persistent_tmpdir (void);
 extern void guestfs___print_timestamped_argv (guestfs_h *g, const char *argv[]);
 extern void guestfs___print_timestamped_message (guestfs_h *g, const char *fs, ...);
 extern void guestfs___free_inspect_info (guestfs_h *g);
diff --git a/src/guestfs.pod b/src/guestfs.pod
index ab4e768d..b8b8ca22 100644
--- a/src/guestfs.pod
+++ b/src/guestfs.pod
@@ -2501,12 +2501,13 @@ has the same effect as calling C<guestfs_set_trace (g, 1)>.
 
 =item TMPDIR
 
-Location of temporary directory, defaults to C</tmp>.
+Location of temporary directory, defaults to C</tmp> except for the
+cached supermin appliance which defaults to C</var/tmp>.
 
 If libguestfs was compiled to use the supermin appliance then the
 real appliance is cached in this directory, shared between all
 handles belonging to the same EUID.  You can use C<$TMPDIR> to
-configure another directory to use in case C</tmp> is not large
+configure another directory to use in case C</var/tmp> is not large
 enough.
 
 =back
diff --git a/src/launch.c b/src/launch.c
index e009aae1..a7a86b97 100644
--- a/src/launch.c
+++ b/src/launch.c
@@ -770,6 +770,7 @@ guestfs__launch (guestfs_h *g)
 
 /* Return the location of the tmpdir (eg. "/tmp") and allow users
  * to override it at runtime using $TMPDIR.
+ * http://www.pathname.com/fhs/pub/fhs-2.3.html#TMPTEMPORARYFILES
  */
 const char *
 guestfs_tmpdir (void)
@@ -788,6 +789,23 @@ guestfs_tmpdir (void)
   return tmpdir;
 }
 
+/* Return the location of the persistent tmpdir (eg. "/var/tmp") and
+ * allow users to override it at runtime using $TMPDIR.
+ * http://www.pathname.com/fhs/pub/fhs-2.3.html#VARTMPTEMPORARYFILESPRESERVEDBETWEE
+ */
+const char *
+guestfs___persistent_tmpdir (void)
+{
+  const char *tmpdir;
+
+  tmpdir = "/var/tmp";
+
+  const char *t = getenv ("TMPDIR");
+  if (t) tmpdir = t;
+
+  return tmpdir;
+}
+
 /* Compute Y - X and return the result in milliseconds.
  * Approximately the same as this code:
  * http://www.mpp.mpg.de/~huber/util/timevaldiff.c