[Libguestfs] [nbdkit PATCH v2 1/3] server: Add nbdkit_stdio_safe

[Eric Blake]

On 4/14/20 2:47 AM, Richard W.M. Jones wrote:
> On Mon, Apr 13, 2020 at 07:28:59PM -0500, Eric Blake wrote:
> [...]
> 
> This patch is fine and can be pushed if you want, but I've got some
> small comments.
> 
>> +If C<nbdkit_stdio_safe> returns true, the value of the configuration
>> +parameter may be used to trigger reading additional data through stdin
>> +(such as a password or inline script).
> 
> I wonder if we want to say "returns 1" rather than true, to give
> ourselves wiggle room in future in case we suddenly decided that we
> needed this to return an error indication?  On the other hand, maybe
> errors can never happen in any conceivable situation.

Sure, I can clean up the wording.

> 
>> @@ -455,6 +467,10 @@ nbdkit_read_password (const char *value, char **password)
>>
>>       if (nbdkit_parse_int ("password file descriptor", &value[1], &fd) == -1)
>>         return -1;
>> +    if (!nbdkit_stdio_safe () && fd < STDERR_FILENO) {
> 
> I think this could be clearer written the other way around:
> 
>      if (fd < STDERR_FILENO && !nbdkit_stdio_safe ()) {
> 
> but then thinking about this more, why isn't it this?
> 
>      if (fd == STDIN_FILENO && !nbdkit_stdio_safe ()) {

nbdkit_stdio_safe controls not only whether you should avoid reading 
stdin, but also whether you should avoid writing to stdout.  Then again, 
no one in their right mind tries to read a password from stdout (even 
when it is opened bi-directionally), and nbdkit_read_password is only 
about reading.  So limiting to fd == STDIN_FILENO doesn't seem too bad.

> 
> Anyway, these are minor points, ACK.
> 
> Rich.
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org