Re: [PATCH v15 08/20] multi-process: add qio channel read function

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Dec 22, 2020 at 10:14:43PM -0800, elena.ufimtseva@oracle.com wrote:
> From: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> 
> Adds qio_channel_readv_full_all() to read both data and FDs.
> Refactors existing code to use this function.
> 
> Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
> Signed-off-by: John G Johnson <john.g.johnson@oracle.com>
> Signed-off-by: Jagannathan Raman <jag.raman@oracle.com>
> ---
>  include/io/channel.h | 25 +++++++++++++
>  io/channel.c         | 85 +++++++++++++++++++++++++++++++-------------
>  2 files changed, 85 insertions(+), 25 deletions(-)
> 
> diff --git a/include/io/channel.h b/include/io/channel.h
> index 2378567d4b..429ece9a05 100644
> --- a/include/io/channel.h
> +++ b/include/io/channel.h
> @@ -774,6 +774,31 @@ void qio_channel_set_aio_fd_handler(QIOChannel *ioc,
>                                      IOHandler *io_write,
>                                      void *opaque);
>  
> +/**
> + * qio_channel_readv_full_all:
> + * @ioc: the channel object
> + * @iov: the array of memory regions to read data to
> + * @niov: the length of the @iov array
> + * @fds: an array of file handles to read
> + * @nfds: number of file handles in @fds
> + * @errp: pointer to a NULL-initialized error object
> + *
> + *
> + * Behaves like qio_channel_readv_full but will attempt
> + * to read all data specified (file handles and memory regions).
> + * The function will wait for all requested data
> + * to be read, yielding from the current coroutine
> + * if required.
> + *
> + * Returns: 0 if all bytes were read, or -1 on error
> + */
> +
> +int qio_channel_readv_full_all(QIOChannel *ioc,
> +                                const struct iovec *iov,
> +                                size_t niov,
> +                                int **fds, size_t *nfds,
> +                                Error **errp);

There parameters are one character mis-aligned here.

> diff --git a/io/channel.c b/io/channel.c
> index bde1f6d0f4..5edaea1fac 100644
> --- a/io/channel.c
> +++ b/io/channel.c
> @@ -91,11 +91,49 @@ int qio_channel_readv_all_eof(QIOChannel *ioc,
>                                const struct iovec *iov,
>                                size_t niov,
>                                Error **errp)
> +{
> +    int ret = qio_channel_readv_full_all(ioc, iov, niov, NULL, NULL, errp);
> +
> +    if (ret == -ECANCELED) {
> +        error_prepend(errp,
> +                      "Unexpected end-of-file before all bytes were read: ");
> +        ret = -1;
> +    }
> +
> +    return ret;
> +}
> +
> +int qio_channel_readv_all(QIOChannel *ioc,
> +                          const struct iovec *iov,
> +                          size_t niov,
> +                          Error **errp)
> +{
> +    int ret = qio_channel_readv_all_eof(ioc, iov, niov, errp);
> +
> +    if (ret == 0) {
> +        error_setg(errp,
> +                   "Unexpected end-of-file before all bytes were read");
> +        return -1;
> +    }
> +    if (ret == 1) {
> +        return 0;
> +    }
> +
> +    return ret;
> +}
> +
> +int qio_channel_readv_full_all(QIOChannel *ioc,
> +                                const struct iovec *iov,
> +                                size_t niov,
> +                                int **fds, size_t *nfds,
> +                                Error **errp)
>  {
>      int ret = -1;
>      struct iovec *local_iov = g_new(struct iovec, niov);
>      struct iovec *local_iov_head = local_iov;
>      unsigned int nlocal_iov = niov;
> +    int **local_fds = fds;
> +    size_t *local_nfds = nfds;

It doesn't look like we actually need these as local variables,
as opposed to just replacing the parameters.

>      bool partial = false;
>  
>      nlocal_iov = iov_copy(local_iov, nlocal_iov,
> @@ -104,7 +142,8 @@ int qio_channel_readv_all_eof(QIOChannel *ioc,
>  
>      while (nlocal_iov > 0) {
>          ssize_t len;
> -        len = qio_channel_readv(ioc, local_iov, nlocal_iov, errp);
> +        len = qio_channel_readv_full(ioc, local_iov, nlocal_iov, local_fds,
> +                                     local_nfds, errp);
>          if (len == QIO_CHANNEL_ERR_BLOCK) {
>              if (qemu_in_coroutine()) {
>                  qio_channel_yield(ioc, G_IO_IN);
> @@ -112,20 +151,33 @@ int qio_channel_readv_all_eof(QIOChannel *ioc,
>                  qio_channel_wait(ioc, G_IO_IN);
>              }
>              continue;
> -        } else if (len < 0) {
> -            goto cleanup;
> -        } else if (len == 0) {
> -            if (partial) {
> -                error_setg(errp,
> -                           "Unexpected end-of-file before all bytes were read");
> +        }
> +
> +        if (len <= 0) {
> +            size_t fd_idx = nfds ? *nfds : 0;
> +            if (partial && (len == 0)) {
> +                ret = -ECANCELED;

As Marc-Andre mentioned, we intentionally avoid returning 'errno' from
any of the QIO functions, so I definitely don't want to see this added.

If I look at the current set of APIs:

qio_channel_readv_full

qio_channel_readv
qio_channel_readv_all
qio_channel_readv_all_eof

qio_channel_read
qio_channel_read_all
qio_channel_read_all_eof

I think the problem is that you're introducing just 1 new function,
when we really should have two in order to complete the code pattern
we have. ie

  qio_channel_readv_full_all
  qio_channel_readv_full_all_eof

the former should call the latter.


>              } else {
> -                ret = 0;
> +                ret = len;
> +            }
> +
> +            while (fds && fd_idx) {
> +                close(*fds[fd_idx - 1]);
> +                fd_idx--;
> +            }
> +
> +            if (fds) {
> +                g_free(*fds);
>              }
> +
>              goto cleanup;
>          }
>  
>          partial = true;
>          iov_discard_front(&local_iov, &nlocal_iov, len);
> +
> +        local_fds = NULL;
> +        local_nfds = 0;
>      }
>  
>      ret = 1;
> @@ -135,23 +187,6 @@ int qio_channel_readv_all_eof(QIOChannel *ioc,
>      return ret;
>  }
>  
> -int qio_channel_readv_all(QIOChannel *ioc,
> -                          const struct iovec *iov,
> -                          size_t niov,
> -                          Error **errp)
> -{
> -    int ret = qio_channel_readv_all_eof(ioc, iov, niov, errp);
> -
> -    if (ret == 0) {
> -        ret = -1;
> -        error_setg(errp,
> -                   "Unexpected end-of-file before all bytes were read");
> -    } else if (ret == 1) {
> -        ret = 0;
> -    }
> -    return ret;
> -}
> -

Try not to mix in code movement with functional changes, as it obscures
the diffs. IOW, if you want to re-arrange funtions in the file, do this
as a separate patch first.


Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|