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Read random sector to avoid cache when spinning up disk

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This commit is contained in:
Andrea Mazzoleni 2026-01-05 16:22:49 +01:00
parent d46a2402b6
commit 0aafcd1819
1 changed files with 41 additions and 2 deletions
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43
cmdline/unix.c
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@ -1620,6 +1620,18 @@ static int devup(dev_t device, const char* name)
int ret;
int f;
void* buf;
uint64_t size;
uint64_t offset;
uint64_t pseudo_random;
/* get a pseudo random number */
ret = randomize(&pseudo_random, sizeof(pseudo_random));
if (ret < 0) {
/* LCOV_EXCL_START */
log_fatal("Failed to retrieve random values.\n");
exit(EXIT_FAILURE);
/* LCOV_EXCL_STOP */
}
if (devresolve(device, file, sizeof(file)) != 0) {
/* LCOV_EXCL_START */
@ -1629,7 +1641,7 @@ static int devup(dev_t device, const char* name)
}
/* O_DIRECT requires memory aligned to the block size */
if (posix_memalign(&buf, 512, 512) != 0) {
if (posix_memalign(&buf, 4096, 4096) != 0) {
/* LCOV_EXCL_START */
log_fatal("Failed to allocate aligned memory for device '%u:%u'.\n", major(device), minor(device));
return -1;
@ -1646,7 +1658,34 @@ static int devup(dev_t device, const char* name)
/* LCOV_EXCL_STOP */
}
ret = read(f, buf, 512);
if (ioctl(f, BLKGETSIZE64, &size) < 0) {
/* LCOV_EXCL_START */
close(f);
free(buf);
log_tag("device:%s:%s:error:%d\n", file, name, errno);
log_fatal("Failed to get device size '%u:%u'.\n", major(device), minor(device));
return -1;
/* LCOV_EXCL_STOP */
}
/* select a random offset */
offset = (pseudo_random % (size / 4096)) * 4096;
#if HAVE_POSIX_FADVISE
/* clear cache */
ret = posix_fadvise(f, offset, 4096, POSIX_FADV_DONTNEED);
if (ret != 0) {
/* LCOV_EXCL_START */
close(f);
free(buf);
log_tag("device:%s:%s:error:%d\n", file, name, errno);
log_fatal("Failed to advise device '%u:%u'.\n", major(device), minor(device));
return -1;
/* LCOV_EXCL_STOP */
}
#endif
ret = pread(f, buf, 4096, offset);
if (ret < 0) {
/* LCOV_EXCL_START */
close(f);