On Wed, Oct 27, 2021 at 8:45 PM Laszlo Ersek <lersek(a)redhat.com> wrote:
...
(hopefully that means nbdkit_error is thread-safe)
> + return ! cmd->error ? 0 : -1;
(6) Using the ! operator with the ternary operator ?: is awkward IMO;
how about just
return cmd->error ? -1 : 0;
cmd->failed is more consistent, but I think we should get rid of this field.
> +}
> +
> +/* Add an extent to the list of extents. */
> +static int
> +add_extent (struct nbdkit_extents *extents,
> + uint64_t *position, uint64_t next_position, bool is_hole)
> +{
> + uint32_t type = 0;
> + const uint64_t length = next_position - *position;
> +
> + if (is_hole) {
> + type = NBDKIT_EXTENT_HOLE;
> + /* Images opened as single link might be backed by another file in the
> + chain, so the holes are not guaranteed to be zeroes. */
> + if (!single_link)
> + type |= NBDKIT_EXTENT_ZERO;
> + }
> +
> + assert (*position <= next_position);
> + if (*position == next_position)
> + return 0;
> +
> + if (vddk_debug_extents)
> + nbdkit_debug ("adding extent type %s at [%" PRIu64 "...%"
PRIu64 "]",
> + is_hole ? "hole" : "allocated data",
> + *position, next_position-1);
> + if (nbdkit_add_extent (extents, *position, length, type) == -1)
> + return -1;
> +
> + *position = next_position;
> + return 0;
> +}
> +
> +/* Asynchronous commands are completed when this function is called. */
> +static void
> +complete_command (void *vp, VixError err)
> +{
> + struct command *cmd = vp;
> +
> + if (err != VIX_OK) {
> + VDDK_ERROR (err, "asynchronous %s failed", command_type_string
(cmd->type));
> + cmd->error = true;
> + }
> +
> + ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&cmd->mutex);
> + cmd->completed = true;
> + pthread_cond_signal (&cmd->cond);
> +}
Seems OK. The ordering seems to match the counterpart in
send_command_and_wait().
(7) Suggestion: in the definition of "struct command", document that the
mutex & condvar protect the "completed" field, and that "error"
is only
meaningful once "completed" is set. (From the current comments on the
fields, I wasn't initially sure whether "error" should be checked
independently of "completed".)
The real issue is having 2 fields to manage the state, allowing
4 possible states, when only 2 states are valid.
We can replace the fields with:
enum command_state { STATE_QUEUED, STATE_RUNNING, STATE_SUCCEEDED,
STATE_FAILED };
...
struct command {
enum command_state state
I did not have time to review the rest of the patch.
Nir