This was introduced two years ago when the getrandom/getentropy API
question was still open, and removed because the discussion was
ongoing. Now getentropy is more widely adopted and soon to be in
POSIX. So reintroduce the symbol into libc since we'll be keeping it
anyway. Discussion of details of the semantics, as interpreted by
NetBSD, is ongoing, but the symbol needs to get in before the
netbsd-10 branch. The draft POSIX text is
(https://www.opengroup.org/austin/docs/austin_1110.pdf):
SYNOPSIS
#include <unistd.h>
int getentropy(void *buffer, size_t length);
DESCRIPTION
The getentropy() function shall write length bytes of data
starting at the location pointed to by buffer. The output
shall be unpredictable high quality random data, generated by
a cryptographically secure pseudo-random number
generator. The maximum permitted value for the length
argument is given by the {GETENTROPY_MAX} symbolic constant
defined in <limits.h>.
RETURN VALUES
Upon successful completion, getentropy() shall return 0;
otherwise, -1 shall be retunred and errno set to indicate the
error.
ERRORS
The getentropy() function shall fail if:
[EINVAL] The value of length is greater than
{GETENTROPY_MAX}.
The getentropy() function may fail if:
[ENOSYS] The system does not provide the necessary
source of entropy.
RATIONALE
The getentropy() function is not a cancellation point.
Minor changes from the previous introduction of getentropy into libc:
- Return EINVAL, not EIO, on buflen > 256.
- Define GETENTROPY_MAX in limits.h.
The declaration of getentropy in unistd.h and definition of
GETENTROPY_MAX in limits.h are currently conditional on
_NETBSD_SOURCE. When the next revision of POSIX is finalized, we can
expose them also under _POSIX_C_SOURCE > 20yymmL as usual -- and this
can be done as a pullup without breaking existing compiled programs.
Posted to tech-userlevel@ a week ago and reviewed by riastradh@.
GETENTROPY(3) Library Functions Manual GETENTROPY(3)
NAME
getentropy - fill a buffer with high quality random data
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
getentropy(void *buf, size_t buflen);
DESCRIPTION
The getentropy() function fills a buffer with high quality random data,
suitable for seeding cryptographically secure psuedorandom number
generators.
getentropy() is only intended for seeding random number generators and is
not intended for use by regular code which simply needs secure random
data. For this purpose, please use arc4random(3).
The maximum value for buflen is 256 bytes.
IMPLEMENTATION NOTES
getentropy() reads from the sysctl(7) variable kern.arandom.
RETURN VALUES
The getentropy() function returns 0 on success, and -1 if an error
occurred.
ERRORS
getentropy() will succeed unless:
[EFAULT] The buf argument points to an invalid memory address.
[EIO] Too many bytes were requested.
SEE ALSO
arc4random(3), rnd(4)
STANDARDS
The getentropy() function is non-standard.
HISTORY
The getentropy() function first appeared in OpenBSD 5.6, then in
FreeBSD 12.0, and NetBSD 10.
unistd.h and libc, and add a man page.
Allow wiggle room in the man page for implementations of fallocate
that either (a) don't fully unwind on failure, leaving new blocks
allocated without changing the file size, or (b) create only in-memory
transient reservations that disappear when crashing or rebooting.
Also, add crossreference to fdiscard from ftruncate(2), and remove the
old BUGS entry from there that called for a generalized version that
allows discarding ranges of a file: that's what fdiscard is.
unimplemented, except enough of linkat(2) to hardlink to a symlink.
Everything new in headers is guarded #ifdef _INCOMPLETE_XOPEN_C063 since
some software (e.g.: xcvs in our own tree) will assume they can use openat(2)
when AT_FDCWD is defined. _INCOMPLETE_XOPEN_C063 will go away once support
will be completed.
set close-on-exec on creation (http://udrepper.livejournal.com/20407.html).
- Add F_DUPFD_CLOEXEC to fcntl(2).
- Add MSG_CMSG_CLOEXEC to recvmsg(2) for unix file descriptor passing.
- Add dup3(2) syscall with a flags argument for O_CLOEXEC, O_NONBLOCK.
- Add pipe2(2) syscall with a flags argument for O_CLOEXEC, O_NONBLOCK.
- Add flags SOCK_CLOEXEC, SOCK_NONBLOCK to the socket type parameter
for socket(2) and socketpair(2).
- Add new paccept(2) syscall that takes an additional sigset_t to alter
the sigmask temporarily and a flags argument to set SOCK_CLOEXEC,
SOCK_NONBLOCK.
- Add new mode character 'e' to fopen(3) and popen(3) to open pipes
and file descriptors for close on exec.
- Add new kqueue1(2) syscall with a new flags argument to open the
kqueue file descriptor with O_CLOEXEC, O_NONBLOCK.
* Fix the system calls that take socklen_t arguments to actually do so.
* Don't include userland header files (signal.h) from system header files
(rump_syscallargs.h).
* Bump libc version for the new syscalls.
christos