[Libguestfs] [PATCH v3] New API: guestfs_device_name returning the drive name

[Richard W.M. Jones]

For each drive added, return the name.  For example calling this with
index 0 will return the string "/dev/sda".  I called it
guestfs_device_name (not drive_name) for consistency with the existing
guestfs_device_index function.

You don't really need to call this function.  You can follow the
advice here:
https://libguestfs.org/guestfs.3.html#block-device-naming
and assume that drives are added with predictable names like
"/dev/sda", "/dev/sdb", etc.

However it's useful to expose the internal guestfs_int_drive_name
function since especially handling names beyond index 26 is tricky
(https://rwmj.wordpress.com/2011/01/09/how-are-linux-drives-named-beyond-drive-26-devsdz/)

Fixes: https://github.com/libguestfs/libguestfs/issues/80
---
 generator/actions_core.ml | 24 +++++++++++++++++++++++-
 lib/drives.c              | 15 +++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/generator/actions_core.ml b/generator/actions_core.ml
index ce9ee39cca..dc12fdc33e 100644
--- a/generator/actions_core.ml
+++ b/generator/actions_core.ml
@@ -737,7 +737,29 @@ returns the index of the device in the list of devices.
 Index numbers start from 0.  The named device must exist,
 for example as a string returned from C<guestfs_list_devices>.
 
-See also C<guestfs_list_devices>, C<guestfs_part_to_dev>." };
+See also C<guestfs_list_devices>, C<guestfs_part_to_dev>,
+C<guestfs_device_name>." };
+
+  { defaults with
+    name = "device_name"; added = (1, 49, 1);
+    style = RString (RPlainString, "name"), [Int "index"], [];
+    tests = [
+      InitEmpty, Always, TestResult (
+        [["device_name"; "0"]], "STREQ (ret, \"/dev/sda\")"), [];
+      InitEmpty, Always, TestResult (
+        [["device_name"; "1"]], "STREQ (ret, \"/dev/sdb\")"), [];
+      InitEmpty, Always, TestLastFail (
+        [["device_name"; "99"]]), []
+    ];
+    shortdesc = "convert device index to name";
+    longdesc = "\
+This function takes a device index and returns the device
+name.  For example index C<0> will return the string C</dev/sda>.
+
+The drive index must have been added to the handle.
+
+See also C<guestfs_list_devices>, C<guestfs_part_to_dev>,
+C<guestfs_device_index>." };
 
   { defaults with
     name = "shutdown"; added = (1, 19, 16);
diff --git a/lib/drives.c b/lib/drives.c
index fd95308d2d..a6179fc367 100644
--- a/lib/drives.c
+++ b/lib/drives.c
@@ -31,6 +31,7 @@
 #include <netdb.h>
 #include <arpa/inet.h>
 #include <assert.h>
+#include <errno.h>
 #include <libintl.h>
 
 #include "c-ctype.h"
@@ -1084,3 +1085,17 @@ guestfs_impl_device_index (guestfs_h *g, const char *device)
     error (g, _("%s: device not found"), device);
   return r;
 }
+
+char *
+guestfs_impl_device_name (guestfs_h *g, int index)
+{
+  char drive_name[64];
+
+  if (index < 0 || index >= g->nr_drives) {
+    guestfs_int_error_errno (g, EINVAL, _("drive index out of range"));
+    return NULL;
+  }
+
+  guestfs_int_drive_name (index, drive_name);
+  return safe_asprintf (g, "/dev/sd%s", drive_name);
+}
-- 
2.35.1