Re: [PATCH] migration/multifd: Document two places for mapped-ram

[Prasad Pandit]

Hello Petr,

On Fri, 1 Mar 2024 at 14:46, <peterx@redhat.com> wrote:
> +         * An explicitly close() on the channel here is normally not

explicitly -> explicit

> +         * required, but can be helpful for "file:" iochannels, where it
> +         * will include an fdatasync() to make sure the data is flushed to
> +         * the disk backend.

* an fdatasync() -> fdatasync()

* qio_channel_close
    -> ioc_klass->io_close = qio_channel_file_close;
     -> qemu_close(fioc->fd)
      -> close(fd);

It does not seem to call fdatasync() before close(fd);

    - qio_channel_file_new_path(filename, O_CREAT | O_WRONLY | O_TRUNC, ...)

Maybe the qio_channel..() calls above should include the 'O_DSYNC'
flag as well? But that will do fdatasync() work at each write(2) call
I think, not sure if that is okay.

> +         *
> +         * The object_unref() cannot guarantee that because: (1) finalize()
> +         * of the iochannel is only triggered on the last reference, and
> +         * it's not guaranteed that we always hold the last refcount when
> +         * reaching here, and, (2) even if finalize() is invoked, it only
> +         * does a close(fd) without data flush.
> +         */

* object_unref
    -> object_finalize
      -> object_deinit
        -> type->instance_finalize
         -> qio_channel_file_finalize
          -> qemu_close(ioc->fd);

* I hope I'm looking at the right code here. (Sorry if I'm not)

Thank you.
---
  - Prasad