On Tue, May 24, 2022 at 12:02:16PM +0100, Daniel P. Berrangé wrote:
> This is for code which needs a portable equivalent to a QIOChannelFile
> connected to /dev/null.
>
> Signed-off-by: Daniel P. Berrangé <berra...@redhat.com>
> ---
> include/io/channel-null.h | 55 +++++++
> io/channel-null.c | 237 ++++++++++++++++++++++++++++++
> io/meson.build | 1 +
> io/trace-events | 3 +
> tests/unit/meson.build | 1 +
> tests/unit/test-io-channel-null.c | 95 ++++++++++++
> 6 files changed, 392 insertions(+)
> create mode 100644 include/io/channel-null.h
> create mode 100644 io/channel-null.c
> create mode 100644 tests/unit/test-io-channel-null.c
> +/**
> + * QIOChannelNull:
> + *
> + * The QIOChannelNull object provides a channel implementation
> + * that discards all writes and returns zero bytes for all reads.
That describes the behavior of /dev/zero, not /dev/null, where reads
always fail with EOF.
> + */
> +
> +struct QIOChannelNull {
> + QIOChannel parent;
> + bool closed;
> +};
> +
> diff --git a/io/channel-null.c b/io/channel-null.c
> +
> +static ssize_t
> +qio_channel_null_readv(QIOChannel *ioc,
> + const struct iovec *iov,
> + size_t niov,
> + int **fds G_GNUC_UNUSED,
> + size_t *nfds G_GNUC_UNUSED,
> + Error **errp)
> +{
> + QIOChannelNull *nioc = QIO_CHANNEL_NULL(ioc);
> +
> + if (nioc->closed) {
> + error_setg_errno(errp, EINVAL,
> + "Channel is closed");
> + return -1;
> + }
> +
> + return 0;
> +}
But this behavior is returning early EOF instead of using iov_memset()
to read all zeroes the way /dev/zero would.
> +++ b/tests/unit/test-io-channel-null.c
> +static void test_io_channel_null_io(void)
> +{
> + g_autoptr(QIOChannelNull) null = qio_channel_null_new();
> + char buf[1024];
> + GIOCondition gotcond = 0;
> + Error *local_err = NULL;
> +
> + g_assert(qio_channel_write(QIO_CHANNEL(null),
> + "Hello World", 11,
> + &error_abort) == 11);
I still cringe seeing tests inside g_assert(), but this is not the
first instance of it.
> +
> + g_assert(qio_channel_read(QIO_CHANNEL(null),
> + buf, sizeof(buf),
> + &error_abort) == 0);
Okay, you're testing for /dev/null behavior of early EOF.
Other than misleading comments, this looks reasonable. But those
comments are core enough as to what this channel does that I don't
feel comfortable giving R-b yet.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
