Re: getrandom: Fail with ENOSYS when the system has no randomness source

[Bruno Haible]

Paul Eggert wrote:
> On 5/9/21 7:51 AM, Bruno Haible wrote:
> >         if (fd < 0)
> > -        return fd;
> > +        {
> > +          errno = ENOSYS;
> > +          return -1;
> > +        }
> 
> If 'open' fails with errno equal to (say) EINTR or EAGAIN or EMFILE, 
> this doesn't mean the operating system lacks a randomness source; it 
> merely means the 'open' failed. And the libc manual allows getrandom to 
> fail with EMFILE or with any other valid error number. (FWIW, the Hurd 
> implementation of getrandom simply passes the errno of 'open' through.)
> 
> How about if we instead change that code to something like this:
> 
>   if (fd < 0)
>     {
>        if (errno == ENOENT || errno == ENOTDIR)
>          errno = ENOSYS;
>        return fd;
>     }
> 
> That is, if /dev/random (or whatever) doesn't exist, we assume the OS is 
> like IRIX and lacks randomness support, so we fail with ENOSYS; 
> otherwise we pass errno through as that's more useful to the caller.

Good point. Thanks for the correction. Done:


2021-05-13  Bruno Haible  <bruno@clisp.org>

        getrandom: Produce a better error code.
        Reported by Paul Eggert in
        <https://lists.gnu.org/archive/html/bug-gnulib/2021-05/msg00025.html>.
        * lib/getrandom.c (getrandom): When open() fails with an error that does
        not indicate the absence of the file, fail with that error code, not
        with ENOSYS.

diff --git a/lib/getrandom.c b/lib/getrandom.c
index 6160118..9e90e64 100644
--- a/lib/getrandom.c
+++ b/lib/getrandom.c
@@ -179,7 +179,8 @@ getrandom (void *buffer, size_t length, unsigned int flags)
       fd = open (randdevice[devrandom], oflags);
       if (fd < 0)
         {
-          errno = ENOSYS;
+          if (errno == ENOENT || errno == ENOTDIR)
+            errno = ENOSYS;
           return -1;
         }
       randfd[devrandom] = fd;