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Re: [Qemu-devel] [PATCH 2/3] io: Add new qio_channel_read{, v}_all_eof f
From: |
Daniel P. Berrange |
Subject: |
Re: [Qemu-devel] [PATCH 2/3] io: Add new qio_channel_read{, v}_all_eof functions |
Date: |
Wed, 6 Sep 2017 09:51:53 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
On Tue, Sep 05, 2017 at 02:11:13PM -0500, Eric Blake wrote:
> Some callers want to distinguish between clean EOF (no bytes read)
> vs. a short read (at least one byte read, but EOF encountered
> before reaching the desired length), as it allows clients the
> ability to do a graceful shutdown when a server shuts down at
> defined safe points in the protocol, rather than treating all
> shutdown scenarios as an error due to EOF. However, we don't want
> to require all callers to have to check for early EOF. So add
> another wrapper function that can be used by the callers that care
> about the distinction.
>
> Signed-off-by: Eric Blake <address@hidden>
> ---
> include/io/channel.h | 53
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
> io/channel.c | 48 +++++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 93 insertions(+), 8 deletions(-)
>
> diff --git a/include/io/channel.h b/include/io/channel.h
> index 8f25893c45..3995e243a3 100644
> --- a/include/io/channel.h
> +++ b/include/io/channel.h
> @@ -269,6 +269,36 @@ ssize_t qio_channel_writev_full(QIOChannel *ioc,
> Error **errp);
>
> /**
> + * qio_channel_readv_all_eof:
> + * @ioc: the channel object
> + * @iov: the array of memory regions to read data into
> + * @niov: the length of the @iov array
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Read data from the IO channel, storing it in the
> + * memory regions referenced by @iov. Each element
> + * in the @iov will be fully populated with data
> + * before the next one is used. The @niov parameter
> + * specifies the total number of elements in @iov.
> + *
> + * The function will wait for all requested data
> + * to be read, yielding from the current coroutine
> + * if required.
> + *
> + * If end-of-file occurs before any data is read,
> + * no error is reported; otherwise, if it occurs
> + * before all requested data has been read, an error
> + * will be reported.
> + *
> + * Returns: 1 if all bytes were read, 0 if end-of-file
> + * occurs without data, or -1 on error
> + */
> +int qio_channel_readv_all_eof(QIOChannel *ioc,
> + const struct iovec *iov,
> + size_t niov,
> + Error **errp);
> +
> +/**
> * qio_channel_readv_all:
> * @ioc: the channel object
> * @iov: the array of memory regions to read data into
> @@ -383,6 +413,28 @@ ssize_t qio_channel_write(QIOChannel *ioc,
> Error **errp);
>
> /**
> + * qio_channel_read_all_eof:
> + * @ioc: the channel object
> + * @buf: the memory region to read data into
> + * @buflen: the number of bytes to @buf
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Reads @buflen bytes into @buf, possibly blocking or (if the
> + * channel is non-blocking) yielding from the current coroutine
> + * multiple times until the entire content is read. If end-of-file
> + * occurs immediately it is not an error, but if it occurs after
> + * data has been read it will return an error rather than a
> + * short-read. Otherwise behaves as qio_channel_read().
> + *
> + * Returns: 1 if all bytes were read, 0 if end-of-file occurs
> + * without data, or -1 on error
> + */
> +int qio_channel_read_all_eof(QIOChannel *ioc,
> + char *buf,
> + size_t buflen,
> + Error **errp);
> +
> +/**
> * qio_channel_read_all:
> * @ioc: the channel object
> * @buf: the memory region to read data into
> @@ -401,6 +453,7 @@ int qio_channel_read_all(QIOChannel *ioc,
> char *buf,
> size_t buflen,
> Error **errp);
> +
> /**
> * qio_channel_write_all:
> * @ioc: the channel object
> diff --git a/io/channel.c b/io/channel.c
> index 9e62794cab..ec4b86de7c 100644
> --- a/io/channel.c
> +++ b/io/channel.c
> @@ -86,16 +86,16 @@ ssize_t qio_channel_writev_full(QIOChannel *ioc,
> }
>
>
> -
> -int qio_channel_readv_all(QIOChannel *ioc,
> - const struct iovec *iov,
> - size_t niov,
> - Error **errp)
> +int qio_channel_readv_all_eof(QIOChannel *ioc,
> + const struct iovec *iov,
> + size_t niov,
> + 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;
> + bool partial = false;
>
> nlocal_iov = iov_copy(local_iov, nlocal_iov,
> iov, niov,
> @@ -114,21 +114,43 @@ int qio_channel_readv_all(QIOChannel *ioc,
> } else if (len < 0) {
> goto cleanup;
> } else if (len == 0) {
> - error_setg(errp,
> - "Unexpected end-of-file before all bytes were read");
> + if (partial) {
> + error_setg(errp,
> + "Unexpected end-of-file before all bytes were
> read");
> + } else {
> + ret = 0;
> + }
> goto cleanup;
> }
>
> + partial = true;
> iov_discard_front(&local_iov, &nlocal_iov, len);
> }
>
> - ret = 0;
> + ret = 1;
>
> cleanup:
> g_free(local_iov_head);
> 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;
> +}
> +
> int qio_channel_writev_all(QIOChannel *ioc,
> const struct iovec *iov,
> size_t niov,
> @@ -205,6 +227,16 @@ ssize_t qio_channel_write(QIOChannel *ioc,
> }
>
>
> +int qio_channel_read_all_eof(QIOChannel *ioc,
> + char *buf,
> + size_t buflen,
> + Error **errp)
> +{
> + struct iovec iov = { .iov_base = buf, .iov_len = buflen };
> + return qio_channel_readv_all_eof(ioc, &iov, 1, errp);
> +}
> +
> +
> int qio_channel_read_all(QIOChannel *ioc,
> char *buf,
> size_t buflen,
Acked-by: Daniel P. Berrange <address@hidden>
Regards,
Daniel
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- [Qemu-devel] [PATCH 0/3] nbd: Use common read/write-all qio functions, Eric Blake, 2017/09/05
- [Qemu-devel] [PATCH 1/3] io: Yield rather than wait when already in coroutine, Eric Blake, 2017/09/05
- [Qemu-devel] [PATCH 2/3] io: Add new qio_channel_read{, v}_all_eof functions, Eric Blake, 2017/09/05
- Re: [Qemu-devel] [PATCH 2/3] io: Add new qio_channel_read{, v}_all_eof functions,
Daniel P. Berrange <=
- [Qemu-devel] [PATCH 3/3] nbd: Use new qio_channel_*_all() functions, Eric Blake, 2017/09/05
- Re: [Qemu-devel] [PATCH 0/3] nbd: Use common read/write-all qio functions, Eric Blake, 2017/09/06