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Added allocation randomization for dynamic wear-leveling

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This implements the second step of full dynamic wear-leveling, block
allocation randomization. This is the key part the uniformly distributes
wear across the filesystem, even through reboots.

The entropy actually comes from the filesystem itself, by xoring
together all of the CRCs in the metadata-pairs on the filesystem. While
this sounds like a ridiculous operation, it's easy to do when we already
scan the metadata-pairs at mount time.

This gives us a random number we can use for block allocation.
Unfortunately it's not a great general purpose random generator as the
output only changes every filesystem write. Fortunately that's exactly
when we need our allocator.

---

Additionally, the randomization created a mess for the testing
framework. Fortunately, this method of randomization is deterministic.
A very useful property for reproducing bugs.
This commit is contained in:
Christopher Haster
2018-08-09 09:06:17 -05:00
parent e4a0d586d5
commit 126ef8b07f
10 changed files with 250 additions and 59 deletions
Download Patch File Download Diff File Expand all files Collapse all files

104
emubd/lfs_emubd.c
View File

@@ -19,6 +19,40 @@
#include <inttypes.h>
// Emulated block device utils
static inline void lfs_emubd_tole32(lfs_emubd_t *emu) {
emu->cfg.read_size = lfs_tole32(emu->cfg.read_size);
emu->cfg.prog_size = lfs_tole32(emu->cfg.prog_size);
emu->cfg.block_size = lfs_tole32(emu->cfg.block_size);
emu->cfg.block_count = lfs_tole32(emu->cfg.block_count);
emu->stats.read_count = lfs_tole32(emu->stats.read_count);
emu->stats.prog_count = lfs_tole32(emu->stats.prog_count);
emu->stats.erase_count = lfs_tole32(emu->stats.erase_count);
for (int i = 0; i < sizeof(emu->history.blocks) /
sizeof(emu->history.blocks[0]); i++) {
emu->history.blocks[i] = lfs_tole32(emu->history.blocks[i]);
}
}
static inline void lfs_emubd_fromle32(lfs_emubd_t *emu) {
emu->cfg.read_size = lfs_fromle32(emu->cfg.read_size);
emu->cfg.prog_size = lfs_fromle32(emu->cfg.prog_size);
emu->cfg.block_size = lfs_fromle32(emu->cfg.block_size);
emu->cfg.block_count = lfs_fromle32(emu->cfg.block_count);
emu->stats.read_count = lfs_fromle32(emu->stats.read_count);
emu->stats.prog_count = lfs_fromle32(emu->stats.prog_count);
emu->stats.erase_count = lfs_fromle32(emu->stats.erase_count);
for (int i = 0; i < sizeof(emu->history.blocks) /
sizeof(emu->history.blocks[0]); i++) {
emu->history.blocks[i] = lfs_fromle32(emu->history.blocks[i]);
}
}
// Block device emulated on existing filesystem
int lfs_emubd_create(const struct lfs_config *cfg, const char *path) {
lfs_emubd_t *emu = cfg->context;
@@ -46,20 +80,39 @@ int lfs_emubd_create(const struct lfs_config *cfg, const char *path) {
}
// Load stats to continue incrementing
snprintf(emu->child, LFS_NAME_MAX, "stats");
snprintf(emu->child, LFS_NAME_MAX, ".stats");
FILE *f = fopen(emu->path, "r");
if (!f) {
return -errno;
memset(&emu->stats, 0, sizeof(emu->stats));
} else {
size_t res = fread(&emu->stats, sizeof(emu->stats), 1, f);
lfs_emubd_fromle32(emu);
if (res < 1) {
return -errno;
}
err = fclose(f);
if (err) {
return -errno;
}
}
size_t res = fread(&emu->stats, sizeof(emu->stats), 1, f);
if (res < 1) {
return -errno;
}
// Load history
snprintf(emu->child, LFS_NAME_MAX, ".history");
f = fopen(emu->path, "r");
if (!f) {
memset(&emu->history, 0, sizeof(emu->history));
} else {
size_t res = fread(&emu->history, sizeof(emu->history), 1, f);
lfs_emubd_fromle32(emu);
if (res < 1) {
return -errno;
}
err = fclose(f);
if (err) {
return -errno;
err = fclose(f);
if (err) {
return -errno;
}
}
return 0;
@@ -161,6 +214,13 @@ int lfs_emubd_prog(const struct lfs_config *cfg, lfs_block_t block,
return -errno;
}
// update history and stats
if (block != emu->history.blocks[0]) {
memcpy(&emu->history.blocks[1], &emu->history.blocks[0],
sizeof(emu->history) - sizeof(emu->history.blocks[0]));
emu->history.blocks[0] = block;
}
emu->stats.prog_count += 1;
return 0;
}
@@ -206,13 +266,15 @@ int lfs_emubd_sync(const struct lfs_config *cfg) {
lfs_emubd_t *emu = cfg->context;
// Just write out info/stats for later lookup
snprintf(emu->child, LFS_NAME_MAX, "config");
snprintf(emu->child, LFS_NAME_MAX, ".config");
FILE *f = fopen(emu->path, "w");
if (!f) {
return -errno;
}
lfs_emubd_tole32(emu);
size_t res = fwrite(&emu->cfg, sizeof(emu->cfg), 1, f);
lfs_emubd_fromle32(emu);
if (res < 1) {
return -errno;
}
@@ -222,13 +284,33 @@ int lfs_emubd_sync(const struct lfs_config *cfg) {
return -errno;
}
snprintf(emu->child, LFS_NAME_MAX, "stats");
snprintf(emu->child, LFS_NAME_MAX, ".stats");
f = fopen(emu->path, "w");
if (!f) {
return -errno;
}
lfs_emubd_tole32(emu);
res = fwrite(&emu->stats, sizeof(emu->stats), 1, f);
lfs_emubd_fromle32(emu);
if (res < 1) {
return -errno;
}
err = fclose(f);
if (err) {
return -errno;
}
snprintf(emu->child, LFS_NAME_MAX, ".history");
f = fopen(emu->path, "w");
if (!f) {
return -errno;
}
lfs_emubd_tole32(emu);
res = fwrite(&emu->history, sizeof(emu->history), 1, f);
lfs_emubd_fromle32(emu);
if (res < 1) {
return -errno;
}