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

[Laszlo Ersek]

On 04/29/22 13:04, Richard W.M. Jones wrote:
> 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);
> +}
> 

Reviewed-by: Laszlo Ersek <lersek at redhat.com>