Libguestfs - Apr 2022 - [PATCH 0/2] lib: Add API for reading the "name" field for a drive

Patch 1 seems uncontroversial.

Patch 2 is tricky.  This is related to the following RFE:
https://github.com/libguestfs/libguestfs/issues/80

I initially believed that the reporter wanted to just associate some
general data per drive, and wanted to reuse the (unused) name field
for this.  That's what this patch implements.

However I since believe that he's in fact trying to just get the drive
name of the drive that was just added.  There's no need for any API
for that, you can just assume drives are called (from the guestfs API
point of view) /dev/sda, /dev/sdb etc.

Adding patch 2 probably confuses things, since I guess most people
would assume that an API called guestfs_get_drive_name would return
the drive name (/dev/sda) not some string that you have to add.

Rich.

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

It is likely this field was never used.  Repurpose it as a general
scratchpad for callers to use to save some per-drive data.

Fixes: https://github.com/libguestfs/libguestfs/issues/80
---
 generator/actions_core.ml | 30 ++++++++++++++++++++++++++++--
 lib/drives.c              | 20 ++++++++++++++++++++
 tests/c-api/tests-main.c  |  4 +++-
 3 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/generator/actions_core.ml b/generator/actions_core.ml
index ce9ee39cca..44b0c22f29 100644
--- a/generator/actions_core.ml
+++ b/generator/actions_core.ml
@@ -263,8 +263,9 @@ deprecated C<guestfs_add_drive_with_if> call (q.v.)
 
 =item C<name>
 
-This field used to be passed as a hint for guest inspection, but
-it is no longer used.
+This is an arbitrary string.  If you pass in a string here, you
+can read it back by calling C<guestfs_get_drive_name>.  It is
+not used by libguestfs itself.
 
 =item C<label>
 
@@ -1507,6 +1508,31 @@ This call is used by L<virt-rescue(1)> to write
directly to
 appliance console (for passing through keystrokes).  It should
 not normally be used by other libguestfs users." };
 
+  { defaults with
+    name = "get_drive_name"; added = (1, 49, 1);
+    style = RString (RPlainString, "name"), [Int "index"],
[];
+    blocking = false;
+    tests = [
+      InitEmpty, Always, TestResult (
+        [["get_drive_name"; "0"]], "STREQ (ret,
\"test\")"), [];
+      InitEmpty, Always, TestLastFail (
+        [["get_drive_name"; "1"]]), [];
+      InitEmpty, Always, TestLastFail (
+        [["get_drive_name"; "99"]]), [];
+    ];
+    shortdesc = "get the drive name";
+    longdesc = "\
+Return the optional C<name> field passed to
C<guestfs_add_drive_opts>
+when n'th drive C<index> was added.
+
+If there is no C<name> field associated with the drive
+then this function returns an error, with error code C<ESRCH>.
+
+If you only have a device name and not an index, you can call
+C<guestfs_device_index>.  If what you want instead is the
+drive name as it appears to libguestfs, there is no function
+for that, instead use C<\"/dev/sda\">,
C<\"/dev/sdb\"> etc." };
+
 ]
 
 let daemon_functions = [
diff --git a/lib/drives.c b/lib/drives.c
index fd95308d2d..0da730c734 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"
@@ -594,6 +595,25 @@ guestfs_int_free_drives (guestfs_h *g)
   g->nr_drives = 0;
 }
 
+char *
+guestfs_impl_get_drive_name (guestfs_h *g, int i)
+{
+  const char *name;
+
+  if (i < 0 || i > g->nr_drives) {
+    guestfs_int_error_errno (g, EINVAL, _("drive index out of
range"));
+    return NULL;
+  }
+
+  name = g->drives[i]->name;
+  if (!name) {
+    guestfs_int_error_errno (g, ESRCH, _("drive does not have a
name"));
+    return NULL;
+  }
+
+  return safe_strdup (g, name);
+}
+
 /**
  * Check string parameter matches regular expression
  * C<^[-_[:alnum:]]+$> (in C locale).
diff --git a/tests/c-api/tests-main.c b/tests/c-api/tests-main.c
index 9e01e4a3dc..a0aad1735d 100644
--- a/tests/c-api/tests-main.c
+++ b/tests/c-api/tests-main.c
@@ -431,7 +431,9 @@ create_handle (void)
     exit (EXIT_FAILURE);
   }
 
-  if (guestfs_add_drive_scratch (g, INT64_C(2)*1024*1024*1024, -1) == -1) {
+  if (guestfs_add_drive_scratch (g, INT64_C(2)*1024*1024*1024,
+                                 GUESTFS_ADD_DRIVE_SCRATCH_NAME,
"test",
+                                 -1) == -1) {
     printf ("FAIL: guestfs_add_drive_scratch\n");
     exit (EXIT_FAILURE);
   }
-- 
2.35.1