Re: [PATCH v20210601 04/38] tools: add readv_exact to libxenctrl

[Juergen Gross <jgross@xxxxxxxx>]

On 01.06.21 18:10, Olaf Hering wrote:
> Read a batch of iovec's.
>
> In the common case of short reads, finish individual iov's with read_exact.
>
> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
> ---
>   tools/libs/ctrl/xc_private.c | 55 +++++++++++++++++++++++++++++++++++-
>   tools/libs/ctrl/xc_private.h |  1 +
>   2 files changed, 55 insertions(+), 1 deletion(-)
>
> diff --git a/tools/libs/ctrl/xc_private.c b/tools/libs/ctrl/xc_private.c
> index d94f846686..ea420b9ba8 100644
> --- a/tools/libs/ctrl/xc_private.c
> +++ b/tools/libs/ctrl/xc_private.c
> @@ -659,8 +659,23 @@ int write_exact(int fd, const void *data, size_t size)
>   
>   #if defined(__MINIOS__)
>   /*
> - * MiniOS's libc doesn't know about writev(). Implement it as multiple 
write()s.
> + * MiniOS's libc doesn't know about readv/writev().
> + * Implement it as multiple read/write()s.
>    */
> +int readv_exact(int fd, const struct iovec *iov, int iovcnt)
> +{
> +    int rc, i;
> +
> +    for ( i = 0; i < iovcnt; ++i )
> +    {
> +        rc = read_exact(fd, iov[i].iov_base, iov[i].iov_len);
> +        if ( rc )
> +            return rc;
> +    }
> +
> +    return 0;
> +}
> +
>   int writev_exact(int fd, const struct iovec *iov, int iovcnt)
>   {
>       int rc, i;
> @@ -675,6 +690,44 @@ int writev_exact(int fd, const struct iovec *iov, int 
> iovcnt)
>       return 0;
>   }
>   #else
> +int readv_exact(int fd, const struct iovec *iov, int iovcnt)
> +{
> +    int rc = 0, idx = 0;
> +    ssize_t len;
> +
> +    while ( idx < iovcnt )
> +    {
> +        len = readv(fd, &iov[idx], min(iovcnt - idx, IOV_MAX));
> +        if ( len == -1 && errno == EINTR )
> +            continue;
> +        if ( len <= 0 )
> +        {
> +            rc = -1;
Is EOF really an error?

> +            goto out;
> +        }
> +        while ( len > 0 && idx < iovcnt )
> +        {
> +            if ( len >= iov[idx].iov_len )
> +            {
> +                len -= iov[idx].iov_len;
> +            }
> +            else
> +            {
> +                void *p = iov[idx].iov_base + len;
> +                size_t l = iov[idx].iov_len - len;
> +
> +                rc = read_exact(fd, p, l);
> +                if ( rc )
> +                    goto out;
> +                len = 0;
This will stop the loop, even if idx hasn't reached iovcnt.

> +            }
> +            idx++;
> +        }
> +    }
> +out:
> +    return rc;
> +}
> +

Juergen

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