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Date: Mon, 1 Jan 2018 22:51:34 +0100
From: Hauke Mehrtens <hauke@...ke-m.de>
To: musl@...ts.openwall.com, Rich Felker <dalias@...c.org>
Subject: Re: [PATCH] Add getrandom syscall wrapper function

On 01/01/2018 09:47 PM, Rich Felker wrote:
> On Mon, Jan 01, 2018 at 09:31:23PM +0100, Hauke Mehrtens wrote:
>> This syscall is available since Linux 3.17 and was also implemented in
>> glibc in version 2.25. This is a pure syscall wrapper liker glibc does
>> it.
>> ---
>>  include/sys/random.h  | 19 +++++++++++++++++++
>>  src/linux/getrandom.c | 11 +++++++++++
>>  2 files changed, 30 insertions(+)
>>  create mode 100644 include/sys/random.h
>>  create mode 100644 src/linux/getrandom.c
>>
>> diff --git a/include/sys/random.h b/include/sys/random.h
>> new file mode 100644
>> index 00000000..5540f877
>> --- /dev/null
>> +++ b/include/sys/random.h
>> @@ -0,0 +1,19 @@
>> +#ifndef _SYS_RANDOM_H
>> +#define _SYS_RANDOM_H
>> +#ifdef __cplusplus
>> +extern "C" {
>> +#endif
>> +
>> +#define __NEED_size_t
>> +#define __NEED_ssize_t
>> +#include <bits/alltypes.h>
>> +
>> +#define GRND_NONBLOCK	0x0001
>> +#define GRND_RANDOM	0x0002
>> +
>> +ssize_t getrandom(void *buf, size_t buflen, unsigned int flags);
>> +
>> +#ifdef __cplusplus
>> +}
>> +#endif
>> +#endif
>> diff --git a/src/linux/getrandom.c b/src/linux/getrandom.c
>> new file mode 100644
>> index 00000000..50b07df9
>> --- /dev/null
>> +++ b/src/linux/getrandom.c
>> @@ -0,0 +1,11 @@
>> +#include <sys/random.h>
>> +#include "syscall.h"
>> +
>> +ssize_t getrandom(void *buf, size_t buflen, unsigned int flags)
>> +{
>> +#ifdef SYS_getrandom
>> +	return syscall_cp(SYS_getrandom, buf, buflen, flags);
>> +#else
>> +	return __syscall_ret(-ENOSYS);
>> +#endif
>> +}
>> -- 
>> 2.11.0
> 
> The #ifdef doesn't make sense; if the definition is missing then it's
> a bug in musl source.

Ok, If I can assume that SYS_getrandom is always defined I will remove this.

> Aside from that I think the patch is okay but I'm not sure it's
> complete. There should probably also be getentropy(),

Adding getentropy() should not be so hard, I can do that.

> and we've
> discussed in the past but never reached any conclusion on whether
> there should be a fallback when the syscall doesn't exist (running on
> old kernel).

glibc does not have a fallback for this syscall there was a long
discussion about this, see here: https://lwn.net/Articles/711013/
As they never found a good solution for their fallback. I think musl
should also not provide a fallback.

This is the glibc implementation:
https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=92dcaa3e2f7bf0f7f1c04cd2fb6a317df1a4e225

Hauke

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