preadv is going to be needed when 'fixed-ram'-enabled stream are to be
restored. Add a minimal implementation of preadv for file channels and
expose it via the generic io_preadv interface.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
 io/channel-file.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/io/channel-file.c b/io/channel-file.c
index e213a0fd7cd2..d2f4706b7f6d 100644
--- a/io/channel-file.c
+++ b/io/channel-file.c
@@ -145,6 +145,32 @@ static ssize_t qio_channel_file_writev(QIOChannel *ioc,
     return ret;
 }
 
+static ssize_t qio_channel_file_preadv(QIOChannel *ioc,
+                                       const struct iovec *iov,
+                                       size_t niov,
+                                       off_t offset,
+                                       Error **errp)
+{
+    QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
+    ssize_t ret;
+
+ retry:
+    ret = preadv(fioc->fd, iov, niov, offset);
+    if (ret < 0) {
+        if (errno == EAGAIN) {
+            return QIO_CHANNEL_ERR_BLOCK;
+        }
+        if (errno == EINTR) {
+            goto retry;
+        }
+
+        error_setg_errno(errp, errno, "Unable to read from file");
+        return -1;
+    }
+
+    return ret;
+}
+
 static ssize_t qio_channel_file_pwritev(QIOChannel *ioc,
                                         const struct iovec *iov,
                                         size_t niov,
@@ -252,6 +278,7 @@ static void qio_channel_file_class_init(ObjectClass *klass,
     ioc_klass->io_readv = qio_channel_file_readv;
     ioc_klass->io_set_blocking = qio_channel_file_set_blocking;
     ioc_klass->io_pwritev = qio_channel_file_pwritev;
+    ioc_klass->io_preadv = qio_channel_file_preadv;
     ioc_klass->io_seek = qio_channel_file_seek;
     ioc_klass->io_close = qio_channel_file_close;
     ioc_klass->io_create_watch = qio_channel_file_create_watch;
-- 
2.34.1

On Fri, Oct 28, 2022 at 01:39:08PM +0300, Nikolay Borisov wrote:
> preadv is going to be needed when 'fixed-ram'-enabled stream are to be
> restored. Add a minimal implementation of preadv for file channels and
> expose it via the generic io_preadv interface.
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  io/channel-file.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/io/channel-file.c b/io/channel-file.c
> index e213a0fd7cd2..d2f4706b7f6d 100644
> --- a/io/channel-file.c
> +++ b/io/channel-file.c
> @@ -145,6 +145,32 @@ static ssize_t qio_channel_file_writev(QIOChannel *ioc,
>      return ret;
>  }
>  
> +static ssize_t qio_channel_file_preadv(QIOChannel *ioc,
> +                                       const struct iovec *iov,
> +                                       size_t niov,
> +                                       off_t offset,
> +                                       Error **errp)
> +{
> +    QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
> +    ssize_t ret;
> +
> + retry:
> +    ret = preadv(fioc->fd, iov, niov, offset);
> +    if (ret < 0) {
> +        if (errno == EAGAIN) {
> +            return QIO_CHANNEL_ERR_BLOCK;
> +        }
> +        if (errno == EINTR) {
> +            goto retry;
> +        }
> +
> +        error_setg_errno(errp, errno, "Unable to read from file");
> +        return -1;
> +    }
> +
> +    return ret;
> +}
> +
>  static ssize_t qio_channel_file_pwritev(QIOChannel *ioc,
>                                          const struct iovec *iov,
>                                          size_t niov,
> @@ -252,6 +278,7 @@ static void qio_channel_file_class_init(ObjectClass *klass,
>      ioc_klass->io_readv = qio_channel_file_readv;
>      ioc_klass->io_set_blocking = qio_channel_file_set_blocking;
>      ioc_klass->io_pwritev = qio_channel_file_pwritev;
> +    ioc_klass->io_preadv = qio_channel_file_preadv;
>      ioc_klass->io_seek = qio_channel_file_seek;
>      ioc_klass->io_close = qio_channel_file_close;
>      ioc_klass->io_create_watch = qio_channel_file_create_watch;

I'd suggest this patch should just be merged into the patch which
adds the io_pwritev callback.


With regards,
Daniel
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