Re: [Qemu-devel] [PATCH 2/2] win32: add readv/writev emulation

[Stefan Weil <sw@weilnetz.de>]

Am 22.04.2013 20:53, schrieb Paolo Bonzini:
> Commit e9d8fbf (qemu-file: do not use stdio for qemu_fdopen, 2013-03-27)
> introduced a usage of writev, which mingw32 does not have.  Even though
> qemu_fdopen itself is not used on mingw32, the future-proof solution is
> to add an implementation of it.  This is simple and similar to how we
> emulate sendmsg/recvmsg in util/iov.c.
>
> Some files include osdep.h without qemu-common.h, so move the definition
> of iovec to osdep.h too, and include osdep.h from qemu-common.h
> unconditionally (protection against including files when NEED_CPU_H is
> defined is not needed since the removal of AREG0).
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  include/qemu-common.h | 22 ++--------------------
>  include/qemu/osdep.h  | 16 ++++++++++++++++
>  util/iov.c            |  2 +-
>  util/osdep.c          | 42 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 61 insertions(+), 21 deletions(-)
>
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index 3b1873e..2cfb1f0 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -84,20 +84,6 @@
>  # error Unknown pointer size
>  #endif
>  
> -#ifndef CONFIG_IOVEC
> -#define CONFIG_IOVEC
> -struct iovec {
> -    void *iov_base;
> -    size_t iov_len;
> -};
> -/*
> - * Use the same value as Linux for now.
> - */
> -#define IOV_MAX		1024
> -#else
> -#include <sys/uio.h>
> -#endif
> -
>  typedef int (*fprintf_function)(FILE *f, const char *fmt, ...)
>      GCC_FMT_ATTR(2, 3);
>  
> @@ -122,16 +108,12 @@ static inline char *realpath(const char *path, char *resolved_path)
>  void configure_icount(const char *option);
>  extern int use_icount;
>  
> -/* FIXME: Remove NEED_CPU_H.  */
> -#ifndef NEED_CPU_H
> -
>  #include "qemu/osdep.h"
>  #include "qemu/bswap.h"
>  
> -#else
> -
> +/* FIXME: Remove NEED_CPU_H.  */
> +#ifdef NEED_CPU_H
>  #include "cpu.h"
> -
>  #endif /* !defined(NEED_CPU_H) */
>  
>  /* main function, renamed */
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 8b465fd..e2697d6 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -161,6 +161,22 @@ int qemu_close(int fd);
>  int qemu_create_pidfile(const char *filename);
>  int qemu_get_thread_id(void);
>  
> +#ifndef CONFIG_IOVEC
> +struct iovec {
> +    void *iov_base;
> +    size_t iov_len;
> +};
> +/*
> + * Use the same value as Linux for now.
> + */
> +#define IOV_MAX		1024
> +
> +ssize_t readv(int fd, struct iovec *iov, unsigned iov_cnt);
> +ssize_t writev(int fd, struct iovec *iov, unsigned iov_cnt);
> +#else
> +#include <sys/uio.h>
> +#endif
> +
>  #ifdef _WIN32
>  static inline void qemu_timersub(const struct timeval *val1,
>                                   const struct timeval *val2,
> diff --git a/util/iov.c b/util/iov.c
> index d32226d..78bbbe1 100644
> --- a/util/iov.c
> +++ b/util/iov.c
> @@ -99,7 +99,7 @@ size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt)
>  static ssize_t
>  do_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, bool do_send)
>  {
> -#if defined CONFIG_IOVEC && defined CONFIG_POSIX
> +#ifdef CONFIG_POSIX
>      ssize_t ret;
>      struct msghdr msg;
>      memset(&msg, 0, sizeof(msg));
> diff --git a/util/osdep.c b/util/osdep.c
> index bd59ac9..5f306a6 100644
> --- a/util/osdep.c
> +++ b/util/osdep.c
> @@ -406,3 +406,45 @@ bool fips_get_state(void)
>      return fips_enabled;
>  }
>  
> +#ifndef CONFIG_IOVEC
> +/* helper function for iov_send_recv() */
> +static ssize_t
> +readv_writev(int fd, struct iovec *iov, unsigned iov_cnt, bool do_write)
> +{
> +    unsigned i = 0;
> +    ssize_t ret = 0;
> +    while (i < iov_cnt) {
> +        ssize_t r = do_write
> +            ? write(fd, iov[i].iov_base, iov[i].iov_len)
> +            : read(fd, iov[i].iov_base, iov[i].iov_len);
> +        if (r > 0) {
> +            ret += r;
> +        } else if (!r) {
> +            break;
> +        } else if (errno == EINTR) {
> +            continue;
> +        } else {
> +            /* else it is some "other" error,
> +             * only return if there was no data processed. */
> +            if (ret == 0) {
> +                ret = -1;
> +            }
> +            break;
> +        }
> +        i++;
> +    }
> +    return ret;
> +}
> +
> +ssize_t
> +readv(int fd, struct iovec *iov, unsigned iov_cnt)
> +{
> +    return readv_writev(fd, iov, iov_cnt, false);
> +}
> +
> +ssize_t
> +writev(int fd, struct iovec *iov, unsigned iov_cnt)
> +{
> +    return readv_writev(fd, iov, iov_cnt, true);
> +}
> +#endif

Hi Paolo,

your patch looks good, but maybe you could modify the signatures
of readv, writev to match the Linux originals (missing const, use int):

    ssize_t readv(int fd, const struct iovec *iov, int iovcnt);
    ssize_t writev(int fd, const struct iovec *iov, int iovcnt);

In an updated patch the tab characters could be replaced by a space
to make checkpatch.pl happy.

Regards,
Stefan