Re: [PATCH v7 2/6] libs/ctrl: Allow writev_exact() to change the iov array

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/07/2026 8:43 am, Frediano Ziglio wrote:
> @@ -649,70 +649,35 @@ int writev_exact(int fd, const struct iovec *iov, int 
> iovcnt)
>      return 0;
>  }
>  #else
> -int writev_exact(int fd, const struct iovec *iov, int iovcnt)
> +int writev_exact(int fd, struct iovec *iov, int iovcnt)
>  {
> -    struct iovec *local_iov = NULL;
> -    int rc = 0, iov_idx = 0, saved_errno = 0;
> -    ssize_t len;
> +    int rc = 0, iov_idx = 0;
> +    ssize_t len = 0;
>  
>      while ( iov_idx < iovcnt )
>      {
> -        /*
> -         * Skip over iov[] entries with 0 length.
> -         *
> -         * This is needed to cover the case where we took a partial write and
> -         * all remaining vectors are of 0 length.  In such a case, the 
> results
> -         * from writev() are indistinguishable from EOF.
> -         */
> -        while ( iov[iov_idx].iov_len == 0 )
> -            if ( ++iov_idx == iovcnt )
> -                goto out;
> +        /* Check iov[] to see whether we had a partial or complete write. */
> +        if ( len >= iov[iov_idx].iov_len )
> +        {
> +            len -= iov[iov_idx++].iov_len;
> +            continue;
> +        }
> +
> +        /* Partial write of iov[iov_idx]. */
> +        iov[iov_idx].iov_base += len;
> +        iov[iov_idx].iov_len  -= len;
>  
>          len = writev(fd, &iov[iov_idx], min(iovcnt - iov_idx, IOV_MAX));
> -        saved_errno = errno;
>  
>          if ( (len == -1) && (errno == EINTR) )
>              continue;
>          if ( len <= 0 )

You can return -1 here, and ...


>          {
>              rc = -1;
> -            goto out;
> -        }
> -
> -        /* Check iov[] to see whether we had a partial or complete write. */
> -        while ( (len > 0) && (iov_idx < iovcnt) )
> -        {
> -            if ( len >= iov[iov_idx].iov_len )
> -                len -= iov[iov_idx++].iov_len;
> -            else
> -            {
> -                /* Partial write of iov[iov_idx]. Copy iov so we can adjust
> -                 * element iov_idx and resubmit the rest. */
> -                if ( !local_iov )
> -                {
> -                    local_iov = malloc(iovcnt * sizeof(*iov));
> -                    if ( !local_iov )
> -                    {
> -                        saved_errno = ENOMEM;
> -                        rc = -1;
> -                        goto out;
> -                    }
> -
> -                    iov = memcpy(local_iov, iov, iovcnt * sizeof(*iov));
> -                }
> -
> -                local_iov[iov_idx].iov_base += len;
> -                local_iov[iov_idx].iov_len  -= len;
> -                break;
> -            }
> +            break;
>          }
>      }
>  
> -    saved_errno = 0;
> -
> - out:
> -    free(local_iov);
> -    errno = saved_errno;
>      return rc;

... return 0 here in order to drop the rc variable.

I can adjust on commit.  Reviewed-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>

~Andrew