Libguestfs - Apr 2022 - [PATCH v2/alternative 2/2] New API: guestfs_device_name returning the drive name

An alternative to:
https://listman.redhat.com/archives/libguestfs/2022-April/028755.html

Patch 1 is the same as previously posted.

Before commit 3a00c4d179 ("Remove inspection from the C library and
switch to daemon/OCaml implementation") in 2017 the name parameter
passed to add_drive was used by inspection to override the device name
that is determined from fstab.  None of our tools ever actually used
this parameter, and when the inspection code was moved inside the
daemon we stopped using this hint field at all.

So it's no longer used, and likely hasn't been used ever.  Therefore
document that the field does nothing.
---
 generator/actions_core.ml | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/generator/actions_core.ml b/generator/actions_core.ml
index 23a2eabef8..ce9ee39cca 100644
--- a/generator/actions_core.ml
+++ b/generator/actions_core.ml
@@ -263,9 +263,8 @@ deprecated C<guestfs_add_drive_with_if> call (q.v.)
 
 =item C<name>
 
-The name the drive had in the original guest, e.g. F</dev/sdb>.
-This is used as a hint to the guest inspection process if
-it is available.
+This field used to be passed as a hint for guest inspection, but
+it is no longer used.
 
 =item C<label>
 
-- 
2.35.1

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..ecd8b79c65 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 name[64] = "/dev/sd";
+
+  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, &name[7]);
+  return safe_strdup (g, name);
+}
-- 
2.35.1