[libvirt] [PATCH v6 10/19] utils: Implement function to pass a buffer to send via a fd to virCommand

[Daniel P. Berrangé]

On Thu, Jul 25, 2019 at 10:30:24AM -0400, Stefan Berger wrote:
> Implement virCommandSetSendBuffer() that allows the caller to pass a
> file descriptor and buffer to virCommand. virCommand will write the
> buffer into the file descriptor. That file descriptor could be the
> write end of a pipe or one of the file descriptors of a socketpair.
> The other file descriptor should be passed to the launched process to
> read the data from.
> 
> Only implement the function to allocate memory for send buffers
> and to free them later on.
> 
> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
> Reviewed-by: Daniel P. Berrangé <berrange at redhat.com>
> ---
>  src/libvirt_private.syms |  1 +
>  src/util/vircommand.c    | 76 ++++++++++++++++++++++++++++++++++++++++
>  src/util/vircommand.h    |  5 +++
>  3 files changed, 82 insertions(+)
> 
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index cf80ea3e44..e6249caa80 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -1725,6 +1725,7 @@ virCommandSetOutputFD;
>  virCommandSetPidFile;
>  virCommandSetPreExecHook;
>  virCommandSetSELinuxLabel;
> +virCommandSetSendBuffer;
>  virCommandSetUID;
>  virCommandSetUmask;
>  virCommandSetWorkingDirectory;
> diff --git a/src/util/vircommand.c b/src/util/vircommand.c
> index e10ca3eb7c..5dee730826 100644
> --- a/src/util/vircommand.c
> +++ b/src/util/vircommand.c
> @@ -76,6 +76,16 @@ struct _virCommandFD {
>      unsigned int flags;
>  };
>  
> +typedef struct _virCommandSendBuffer virCommandSendBuffer;
> +typedef virCommandSendBuffer *virCommandSendBufferPtr;
> +
> +struct _virCommandSendBuffer {
> +    int fd;
> +    unsigned char *buffer;
> +    size_t buflen;
> +    off_t offset;
> +};
> +
>  struct _virCommand {
>      int has_error; /* ENOMEM on allocation failure, -1 for anything else.  */
>  
> @@ -135,6 +145,9 @@ struct _virCommand {
>      char *appArmorProfile;
>  #endif
>      int mask;
> +
> +    virCommandSendBufferPtr sendBuffers;
> +    size_t numSendBuffers;
>  };
>  
>  /* See virCommandSetDryRun for description for this variable */
> @@ -1728,6 +1741,67 @@ virCommandSetWorkingDirectory(virCommandPtr cmd, const char *pwd)
>  }
>  
>  
> +static int
> +virCommandGetNumSendBuffers(virCommandPtr cmd)
> +{
> +    return cmd->numSendBuffers;
> +}
> +
> +
> +static void
> +virCommandFreeSendBuffers(virCommandPtr cmd)
> +{
> +    size_t i;
> +
> +    for (i = 0; i < virCommandGetNumSendBuffers(cmd); i++) {
> +        VIR_FORCE_CLOSE(cmd->sendBuffers[i].fd);
> +        VIR_FREE(cmd->sendBuffers[i].buffer);
> +    }
> +    VIR_FREE(cmd->sendBuffers);
> +}
> +
> +
> +/**
> + * virCommandSetSendBuffer
> + * @cmd: the command to modify
> + *
> + * Pass a buffer to virCommand that will be written into the
> + * given file descriptor. The buffer will be freed automatically
> + * and the file descriptor closed.
> + */
> +int
> +virCommandSetSendBuffer(virCommandPtr cmd,
> +                        int fd,
> +                        unsigned char *buffer, size_t buflen)
> +{
> +    size_t i = virCommandGetNumSendBuffers(cmd);
> +
> +    if (!cmd || cmd->has_error)
> +        return -1;
> +
> +    if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0) {
> +        virReportSystemError(errno, "%s",
> +                             _("fcntl failed to set O_NONBLOCK"));
> +        cmd->has_error = errno;
> +        return -1;
> +    }

I hit a build failure on mingw with this change, because F_SETFL
doesn't exist.

None of the vircommand code actually runs on windows, so we just
need to stub this method out to immediately return -1 with
has_error set to ENOSUPP i guess.

Thre's another usage of O_NONBLOCK with same problem.


If you can fix this, I'm happy to push the series.

Regards,
Daniel
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