[Libguestfs] [PATCH libnbd 4/8] copy: Separate finishing a command from freeing it

[Eric Blake]

On Sun, Feb 20, 2022 at 02:13:59PM +0200, Nir Soffer wrote:
> free_command() was abused as a completion callback. Introduce
> finish_command() completion callback, so code that want to free a
> command does not have to add dummy errors.
> 
> This will make it easier to manage worker state when a command
> completes.
> 
> Signed-off-by: Nir Soffer <nsoffer at redhat.com>
> ---
>  copy/multi-thread-copying.c | 34 ++++++++++++++++++++--------------
>  1 file changed, 20 insertions(+), 14 deletions(-)

In addition to Rich's review,

>  
>  static int
> -free_command (void *vp, int *error)
> +finished_command (void *vp, int *error)
>  {
>    struct command *command = vp;
> -  struct buffer *buffer = command->slice.buffer;
>  
>    if (*error) {
>      fprintf (stderr, "write at offset %" PRId64 " failed: %s\n",
>               command->offset, strerror (*error));
>      exit (EXIT_FAILURE);
>    }
>  
> +  free_command (command);
> +
> +  return 1; /* auto-retires the command */
> +}
> +
> +static void
> +free_command (struct command *command)
> +{
> +  struct buffer *buffer = command->slice.buffer;

Do we want to allow 'free_command (NULL)', in which case this should
check if command is non-NULL before initializing buffer?  Doing so may
make some other cleanup paths easier to write.

But for now, all callers pass in non-NULL, so ACK either way.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org