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util: don't block on getrandom()

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This commit is contained in:
Lennart Poettering 2014-10-30 15:27:53 +01:00
parent e3c72c21d6
commit 97768fc574
2 changed files with 28 additions and 4 deletions
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8
src/shared/missing.h
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@ -149,6 +149,14 @@ static inline int getrandom(void *buffer, size_t count, unsigned flags) {
}
#endif
#ifndef GRND_NONBLOCK
#define GRND_NONBLOCK 0x0001
#endif
#ifndef GRND_RANDOM
#define GRND_RANDOM 0x0002
#endif
#ifndef BTRFS_IOCTL_MAGIC
#define BTRFS_IOCTL_MAGIC 0x94
#endif

24
src/shared/util.c
View file

@ -2470,10 +2470,17 @@ int dev_urandom(void *p, size_t n) {
int r, fd;
ssize_t k;
/* Use the syscall unless we know we don't have it, or when
* the requested size is too large for it. */
/* Gathers some randomness from the kernel. This call will
* never block, and will always return some data from the
* kernel, regardless if the random pool is fully initialized
* or not. It thus makes no guarantee for the quality of the
* returned entropy, but is good enough for or usual usecases
* of seeding the hash functions for hashtable */
/* Use the getrandom() syscall unless we know we don't have
* it, or when the requested size is too large for it. */
if (have_syscall != 0 || (size_t) (int) n != n) {
r = getrandom(p, n, 0);
r = getrandom(p, n, GRND_NONBLOCK);
if (r == (int) n) {
have_syscall = true;
return 0;
@ -2481,8 +2488,17 @@ int dev_urandom(void *p, size_t n) {
if (r < 0) {
if (errno == ENOSYS)
/* we lack the syscall, continue with reading from /dev/urandom */
/* we lack the syscall, continue with
* reading from /dev/urandom */
have_syscall = false;
else if (errno == EAGAIN)
/* not enough entropy for now. Let's
* remember to use the syscall the
* next time, again, but also read
* from /dev/urandom for now, which
* doesn't care about the current
* amount of entropy. */
have_syscall = true;
else
return -errno;
} else