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Added proper handling of orphans
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Unfortunately, threading all dir blocks in a linked-list did
not come without problems.

While it's possible to atomically add a dir to the linked list
(by adding the new dir into the linked-list position immediately
after it's parent, requiring only one atomic update to the parent
block), it is not easy to make sure the linked-list is in a state
that always allows atomic removal of dirs.

The simple solution is to allow this non-atomic removal, with an
additional step to remove any orphans that could have been created
by a power-loss. This deorphan step is only run if the normal
allocator has failed.
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@geky
geky committed Apr 18, 2017
1 parent 8a67452 commit a3734ee
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Showing 3 changed files with 216 additions and 40 deletions.
32 changes: 14 additions & 18 deletions emubd/lfs_emubd.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,8 @@
#include <dirent.h>
#include <sys/stat.h>
#include <unistd.h>
#include <assert.h>
#include <stdbool.h>


// Block device emulated on existing filesystem
Expand Down Expand Up @@ -76,12 +78,10 @@ int lfs_emubd_read(lfs_emubd_t *emu, lfs_block_t block,
uint8_t *data = buffer;

// Check if read is valid
if (!(off % emu->info.read_size == 0 &&
size % emu->info.read_size == 0 &&
((uint64_t)block*emu->info.erase_size + off + size
< emu->info.total_size))) {
return -EINVAL;
}
assert(off % emu->info.read_size == 0);
assert(size % emu->info.read_size == 0);
assert((uint64_t)block*emu->info.erase_size + off + size
< emu->info.total_size);

// Zero out buffer for debugging
memset(data, 0, size);
Expand Down Expand Up @@ -128,12 +128,10 @@ int lfs_emubd_prog(lfs_emubd_t *emu, lfs_block_t block,
const uint8_t *data = buffer;

// Check if write is valid
if (!(off % emu->info.prog_size == 0 &&
size % emu->info.prog_size == 0 &&
((uint64_t)block*emu->info.erase_size + off + size
< emu->info.total_size))) {
return -EINVAL;
}
assert(off % emu->info.prog_size == 0);
assert(size % emu->info.prog_size == 0);
assert((uint64_t)block*emu->info.erase_size + off + size
< emu->info.total_size);

// Iterate over blocks until enough data is read
while (size > 0) {
Expand Down Expand Up @@ -177,12 +175,10 @@ int lfs_emubd_erase(lfs_emubd_t *emu, lfs_block_t block,
lfs_off_t off, lfs_size_t size) {

// Check if erase is valid
if (!(off % emu->info.erase_size == 0 &&
size % emu->info.erase_size == 0 &&
((uint64_t)block*emu->info.erase_size + off + size
< emu->info.total_size))) {
return -EINVAL;
}
assert(off % emu->info.erase_size == 0);
assert(size % emu->info.erase_size == 0);
assert((uint64_t)block*emu->info.erase_size + off + size
< emu->info.total_size);

// Iterate and erase blocks
while (size > 0) {
Expand Down
167 changes: 145 additions & 22 deletions lfs.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -77,6 +77,7 @@ static int lfs_bd_crc(lfs_t *lfs, lfs_block_t block,

// predeclared filesystem traversal
static int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data);
int lfs_deorphan(lfs_t *lfs);

static int lfs_alloc_lookahead(void *p, lfs_block_t block) {
lfs_t *lfs = p;
Expand Down Expand Up @@ -143,8 +144,24 @@ static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
int err = lfs_alloc_scan(lfs);
if (err) {
return err;
} else if (lfs->free.begin == lfs->free.end) {
return LFS_ERROR_NO_SPACE;
}

if (lfs->free.begin == lfs->free.end) {
// Still can't allocate a block? check for orphans
int err = lfs_deorphan(lfs);
if (err) {
return err;
}

err = lfs_alloc_scan(lfs);
if (err) {
return err;
}

if (lfs->free.begin == lfs->free.end) {
// Ok, it's true, we're out of space
return LFS_ERROR_NO_SPACE;
}
}
}

Expand Down Expand Up @@ -1146,7 +1163,7 @@ static int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
// skip '.' and '..'
dir.off += 2*sizeof(struct lfs_disk_entry) + 3;

// TODO iterate over files
// iterate over contents
while ((0x7fffffff & dir.d.size) >= dir.off + sizeof(file.entry.d)) {
int err = lfs_bd_read(lfs, dir.pair[0], dir.off,
sizeof(file.entry.d), &file.entry.d);
Expand All @@ -1155,14 +1172,7 @@ static int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
}

dir.off += file.entry.d.len;
if ((0xf & file.entry.d.type) == LFS_TYPE_DIR) {
for (int i = 0; i < 2; i++) {
int err = cb(data, file.entry.d.u.dir[i]);
if (err) {
return err;
}
}
} else if ((0xf & file.entry.d.type) == LFS_TYPE_REG) {
if ((0xf & file.entry.d.type) == LFS_TYPE_REG) {
if (file.entry.d.u.file.size < lfs->block_size) {
int err = cb(data, file.entry.d.u.file.head);
if (err) {
Expand All @@ -1189,6 +1199,85 @@ static int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
}
}

int lfs_deorphan(lfs_t *lfs) {
// iterate over all directories
lfs_block_t pred[2] = {0, 1};
lfs_block_t cwd[2] = {lfs->root[0], lfs->root[1]};

while (true) {
lfs_dir_t child;
int err = lfs_dir_fetch(lfs, &child, cwd);
if (err) {
return err;
}

// orphans can only be empty dirs
// there still might be a dir block with this size that isn't
// the head of a directory, so we still have to check for '..'
if (child.d.size == sizeof(child.d) +
2*sizeof(struct lfs_disk_entry) + 3) {
lfs_entry_t entry;
err = lfs_dir_find(lfs, &child, &(const char*){".."}, &entry);
if (err && err != LFS_ERROR_NO_ENTRY) {
return err;
}

// only the head of directories can be orphans
if (err != LFS_ERROR_NO_ENTRY) {
lfs_dir_t dir;
int err = lfs_dir_fetch(lfs, &dir, entry.d.u.dir);
if (err) {
return err;
}

// check if we are any of our parents children
while (true) {
int err = lfs_dir_next(lfs, &dir, &entry);
if (err && err != LFS_ERROR_NO_ENTRY) {
return err;
}

if (err == LFS_ERROR_NO_ENTRY) {
// we are an orphan
LFS_INFO("Found orphan %d %d", cwd[0], cwd[1]);
int err = lfs_dir_fetch(lfs, &dir, pred);
if (err) {
return err;
}

dir.d.tail[0] = child.d.tail[0];
dir.d.tail[1] = child.d.tail[1];
dir.d.rev += 1;

err = lfs_pair_commit(lfs, dir.pair,
1, (struct lfs_commit_region[]) {
{0, sizeof(dir.d), &dir.d},
});
if (err) {
return err;
}

break;
} else if (lfs_paircmp(entry.d.u.dir, cwd) == 0) {
// has parent
break;
}
}
}
}

// to next directory
pred[0] = cwd[0];
pred[1] = cwd[1];
cwd[0] = child.d.tail[0];
cwd[1] = child.d.tail[1];

if (!cwd[0]) {
return 0;
}
}
}

int lfs_remove(lfs_t *lfs, const char *path) {
lfs_dir_t cwd;
int err = lfs_dir_fetch(lfs, &cwd, lfs->cwd);
Expand All @@ -1202,18 +1291,61 @@ int lfs_remove(lfs_t *lfs, const char *path) {
return err;
}

lfs_dir_t dir;
if (entry.d.type == LFS_TYPE_DIR) {
// must be empty before removal
lfs_dir_t dir;
int err = lfs_dir_fetch(lfs, &dir, entry.d.u.dir);
if (err) {
return err;
} else if (dir.d.size != sizeof(dir.d) +
2*sizeof(struct lfs_disk_entry) + 3) {
return LFS_ERROR_INVALID;
}
}

cwd.d.rev += 1;
cwd.d.size -= entry.d.len;

// either shift out the one entry or remove the whole dir block
if (cwd.d.size == sizeof(dir.d)) {
lfs_dir_t pdir;
int err = lfs_dir_fetch(lfs, &pdir, lfs->cwd);
if (err) {
return err;
}

while (lfs_paircmp(pdir.d.tail, cwd.pair) != 0) {
int err = lfs_dir_fetch(lfs, &pdir, pdir.d.tail);
if (err) {
return err;
}
}

pdir.d.tail[0] = cwd.d.tail[0];
pdir.d.tail[1] = cwd.d.tail[1];
pdir.d.rev += 1;

err = lfs_pair_commit(lfs, pdir.pair,
1, (struct lfs_commit_region[]) {
{0, sizeof(pdir.d), &pdir.d},
});
if (err) {
return err;
}
} else {
int err = lfs_pair_shift(lfs, entry.dir,
1, (struct lfs_commit_region[]) {
{0, sizeof(cwd.d), &cwd.d},
},
entry.off, entry.d.len);
if (err) {
return err;
}
}

if (entry.d.type == LFS_TYPE_DIR) {
// remove ourselves from the dir list
// this may create an orphan, which must be deorphaned
lfs_dir_t pdir;
memcpy(&pdir, &cwd, sizeof(pdir));

Expand Down Expand Up @@ -1241,15 +1373,6 @@ int lfs_remove(lfs_t *lfs, const char *path) {
}
}

cwd.d.rev += 1;
cwd.d.size -= entry.d.len;
// TODO remove dir block?

// Drop contents on the floor
return lfs_pair_shift(lfs, entry.dir,
1, (struct lfs_commit_region[]) {
{0, sizeof(cwd.d), &cwd.d},
},
entry.off, entry.d.len);
return 0;
}

57 changes: 57 additions & 0 deletions tests/test_dirs.sh
View file
Original file line number Diff line number Diff line change
Expand Up @@ -123,5 +123,62 @@ tests/test.py << TEST
lfs_unmount(&lfs) => 0;
TEST

echo "--- Directory deletion ---"
tests/test.py << TEST
lfs_mount(&lfs, &config) => 0;
lfs_remove(&lfs, "potato") => LFS_ERROR_INVALID;
lfs_remove(&lfs, "potato/sweet") => 0;
lfs_remove(&lfs, "potato/baked") => 0;
lfs_remove(&lfs, "potato/fried") => 0;
lfs_dir_open(&lfs, &dir[0], "potato") => 0;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, ".") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "..") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 0;
lfs_dir_close(&lfs, &dir[0]) => 0;
lfs_remove(&lfs, "potato") => 0;
lfs_dir_open(&lfs, &dir[0], "/") => 0;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, ".") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "..") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "burito") => 0;
info.type => LFS_TYPE_REG;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "cactus") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 0;
lfs_dir_close(&lfs, &dir[0]) => 0;
lfs_unmount(&lfs) => 0;
TEST
tests/test.py << TEST
lfs_mount(&lfs, &config) => 0;
lfs_dir_open(&lfs, &dir[0], "/") => 0;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, ".") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "..") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "burito") => 0;
info.type => LFS_TYPE_REG;
lfs_dir_read(&lfs, &dir[0], &info) => 1;
strcmp(info.name, "cactus") => 0;
info.type => LFS_TYPE_DIR;
lfs_dir_read(&lfs, &dir[0], &info) => 0;
lfs_dir_close(&lfs, &dir[0]) => 0;
lfs_unmount(&lfs) => 0;
TEST

echo "--- Results ---"
tests/stats.py

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