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Added support for atomically committing custom attributes

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Although it's simple and probably what most users expect, the previous
custom attributes API suffered from one problem: the inability to update
attributes atomically.

If we consider our timestamp use case, updating a file would require:
1. Update the file
2. Update the timestamp

If a power loss occurs during this sequence of updates, we could end up
with a file with an incorrect timestamp.

Is this a big deal? Probably not, but it could be a surprise only found
after a power-loss. And littlefs was developed with the _specifically_
to avoid suprises during power-loss.

The littlefs is perfectly capable of bundling multiple attribute updates
in a single directory commit. That's kind of what it was designed to do.
So all we need is a new committer opcode for list of attributes, and
then poking that list of attributes through the API.

We could provide the single-attribute functions, but don't, because the
fewer functions makes for a smaller codebase, and these are already the
more advanced functions so we can expect more from users. This also
changes semantics about what happens when we don't find an attribute,
since erroring would throw away all of the other attributes we're
processing.

To atomically commit both custom attributes and file updates, we need a
new API, lfs_file_setattr. Unfortunately the semantics are a bit more
confusing than lfs_setattr, since the attributes aren't written out
immediately.
This commit is contained in:
Christopher Haster
2018-04-05 23:23:14 -05:00
parent 6ffc8d3480
commit 6c754c8023
2 changed files with 224 additions and 124 deletions
Download Patch File Download Diff File Expand all files Collapse all files

254
lfs.c
View File

@@ -515,6 +515,7 @@ struct lfs_region {
LFS_FROM_DROP,
LFS_FROM_MEM,
LFS_FROM_REGION,
LFS_FROM_ATTRS,
} type;
lfs_off_t off;
@@ -522,6 +523,12 @@ struct lfs_region {
lfs_ssize_t size;
};
struct lfs_attrs_region {
const struct lfs_attr *attrs;
int count;
lfs_size_t len;
};
struct lfs_region_region {
lfs_block_t block;
lfs_off_t off;
@@ -568,6 +575,73 @@ static int lfs_commit_region(lfs_t *lfs,
newoff += regions[i].size;
break;
}
case LFS_FROM_ATTRS: {
const struct lfs_attrs_region *attrs = regions[i].buffer;
// order doesn't matter, so we write new attrs first. this
// is still O(n^2) but only O(n) disk access
for (int j = 0; j < attrs->count; j++) {
if (attrs->attrs[j].size == 0) {
continue;
}
lfs_entry_attr_t attr = {
.d.type = attrs->attrs[j].type,
.d.len = attrs->attrs[j].size,
};
lfs_crc(crc, &attr.d, sizeof(attr.d));
int err = lfs_bd_prog(lfs, newblock, newoff,
&attr.d, sizeof(attr.d));
if (err) {
return err;
}
lfs_crc(crc,
attrs->attrs[j].buffer, attrs->attrs[j].size);
err = lfs_bd_prog(lfs, newblock, newoff+sizeof(attr.d),
attrs->attrs[j].buffer, attrs->attrs[j].size);
if (err) {
return err;
}
newoff += sizeof(attr.d) + attrs->attrs[j].size;
}
// copy over attributes without updates
lfs_entry_attr_t attr;
for (lfs_off_t k = 0; k < attrs->len; k += 2+attr.d.len) {
int err = lfs_bd_read(lfs, oldblock, oldoff,
&attr.d, sizeof(attr.d));
if (err) {
return err;
}
bool updating = false;
for (int j = 0; j < attrs->count; j++) {
if (attr.d.type == attrs->attrs[j].type) {
updating = true;
}
}
if (!updating) {
err = lfs_commit_region(lfs,
oldblock, oldoff,
newblock, newoff,
0, NULL, 0,
attr.d.len, crc);
if (err) {
return err;
}
newoff += 2+attr.d.len;
}
oldoff += 2+attr.d.len;
}
break;
}
}
i += 1;
@@ -590,6 +664,8 @@ static int lfs_commit_region(lfs_t *lfs,
}
}
// sanity check our commit math
LFS_ASSERT(newoff == end);
return 0;
}
@@ -1044,116 +1120,100 @@ static int lfs_dir_getinfo(lfs_t *lfs,
return 0;
}
static int lfs_dir_getattr(lfs_t *lfs,
static int lfs_dir_getattrs(lfs_t *lfs,
lfs_dir_t *dir, const lfs_entry_t *entry,
uint8_t type, void *buffer, lfs_size_t size) {
const struct lfs_attr *attrs, int count) {
// set to zero in case we can't find the attributes or size mismatch
for (int j = 0; j < count; j++) {
memset(attrs[j].buffer, 0, attrs[j].size);
}
// search for attribute in attribute region
lfs_off_t off = sizeof(dir->d) + lfs_entry_elen(entry);
lfs_off_t i = 0;
while (i < lfs_entry_alen(entry)) {
lfs_attr_t attr;
lfs_off_t off = 4+lfs_entry_elen(entry);
lfs_entry_attr_t attr;
for (lfs_off_t i = 0; i < lfs_entry_alen(entry); i += 2+attr.d.len) {
int err = lfs_dir_get(lfs, dir,
entry->off+off+i, &attr.d, sizeof(attr.d));
if (err) {
return err;
}
if (attr.d.type != type) {
i += attr.d.len;
continue;
for (int j = 0; j < count; j++) {
if (attr.d.type == attrs[j].type) {
if (attr.d.len > attrs[j].size) {
return LFS_ERR_RANGE;
}
err = lfs_dir_get(lfs, dir,
entry->off+off+i+sizeof(attr.d),
attrs[j].buffer, attr.d.len);
if (err) {
return err;
}
}
}
if (attr.d.len > size) {
return LFS_ERR_RANGE;
}
err = lfs_dir_get(lfs, dir,
entry->off+off+i+sizeof(attr.d), buffer, attr.d.len);
if (err) {
return err;
}
return attr.d.len;
}
return LFS_ERR_NODATA;
}
static int lfs_dir_setattr(lfs_t *lfs,
lfs_dir_t *dir, lfs_entry_t *entry,
uint8_t type, const void *buffer, lfs_size_t size) {
// search for attribute in attribute region
lfs_off_t off = sizeof(dir->d) + lfs_entry_elen(entry);
lfs_off_t i = 0;
lfs_size_t oldlen = 0;
while (i < lfs_entry_alen(entry)) {
lfs_attr_t attr;
int err = lfs_dir_get(lfs, dir,
entry->off+off+i, &attr.d, sizeof(attr.d));
if (err) {
return err;
}
if (attr.d.type != type) {
i += attr.d.len;
continue;
}
oldlen = attr.d.len;
break;
}
// make sure the attribute fits
if (lfs_entry_elen(entry) - oldlen + size > lfs->attrs_size ||
(0x7fffffff & dir->d.size) - oldlen + size > lfs->cfg->block_size) {
return LFS_ERR_NOSPC;
}
lfs_attr_t attr;
attr.d.type = type;
attr.d.len = size;
int err = lfs_dir_set(lfs, dir, entry, (struct lfs_region[]){
{LFS_FROM_MEM, off+i, &attr.d, sizeof(attr.d)},
{LFS_FROM_MEM, off+i, buffer, size},
{LFS_FROM_DROP, off+i, NULL, -oldlen}}, 3);
if (err) {
return err;
}
return 0;
}
static int lfs_dir_removeattr(lfs_t *lfs,
lfs_dir_t *dir, lfs_entry_t *entry, uint8_t type) {
// search for attribute in attribute region
lfs_off_t off = sizeof(dir->d) + lfs_entry_elen(entry);
lfs_off_t i = 0;
while (i < lfs_entry_alen(entry)) {
lfs_attr_t attr;
static lfs_ssize_t lfs_dir_checkattrs(lfs_t *lfs,
lfs_dir_t *dir, lfs_entry_t *entry,
const struct lfs_attr *attrs, int count) {
// check that attributes fit
lfs_size_t nsize = 0;
for (int j = 0; j < count; j++) {
nsize += 2+attrs[j].size;
}
lfs_off_t off = 4+lfs_entry_elen(entry);
lfs_entry_attr_t attr;
for (lfs_off_t i = 0; i < lfs_entry_alen(entry); i += 2+attr.d.len) {
int err = lfs_dir_get(lfs, dir,
entry->off+off+i, &attr.d, sizeof(attr.d));
if (err) {
return err;
}
if (attr.d.type != type) {
i += attr.d.len;
continue;
bool updated = false;
for (int j = 0; j < count; j++) {
if (attr.d.type == attrs[j].type) {
updated = true;
}
}
err = lfs_dir_set(lfs, dir, entry, (struct lfs_region[]){
{LFS_FROM_DROP, off+i,
NULL, -(sizeof(attr.d)+attr.d.len)}}, 1);
if (err) {
return err;
if (!updated) {
nsize += 2+attr.d.len;
}
return 0;
}
return LFS_ERR_NODATA;
if (nsize > lfs->attrs_size || (
(0x7fffffff & dir->d.size) + lfs_entry_size(entry) -
lfs_entry_alen(entry) + nsize > lfs->cfg->block_size)) {
return LFS_ERR_NOSPC;
}
return nsize;
}
static int lfs_dir_setattrs(lfs_t *lfs,
lfs_dir_t *dir, lfs_entry_t *entry,
const struct lfs_attr *attrs, int count) {
// make sure attributes fit
lfs_ssize_t nsize = lfs_dir_checkattrs(lfs, dir, entry, attrs, count);
if (nsize < 0) {
return nsize;
}
// commit to entry, majority of work is in LFS_FROM_ATTRS
lfs_size_t oldlen = lfs_entry_alen(entry);
entry->d.alen = (0xc0 & entry->d.alen) | nsize;
return lfs_dir_set(lfs, dir, entry, (struct lfs_region[]){
{LFS_FROM_MEM, 0, &entry->d, 4},
{LFS_FROM_DROP, 0, NULL, -4},
{LFS_FROM_ATTRS, 4+lfs_entry_elen(entry),
&(struct lfs_attrs_region){attrs, count, oldlen}, nsize}}, 3);
}
/// Top level directory operations ///
@@ -2372,8 +2432,8 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
/// Attribute operations ///
int lfs_getattr(lfs_t *lfs, const char *path,
uint8_t type, void *buffer, lfs_size_t size) {
int lfs_getattrs(lfs_t *lfs, const char *path,
const struct lfs_attr *attrs, int count) {
lfs_dir_t cwd;
int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
if (err) {
@@ -2386,11 +2446,11 @@ int lfs_getattr(lfs_t *lfs, const char *path,
return err;
}
return lfs_dir_getattr(lfs, &cwd, &entry, type, buffer, size);
return lfs_dir_getattrs(lfs, &cwd, &entry, attrs, count);
}
int lfs_setattr(lfs_t *lfs, const char *path,
uint8_t type, const void *buffer, lfs_size_t size) {
int lfs_setattrs(lfs_t *lfs, const char *path,
const struct lfs_attr *attrs, int count) {
lfs_dir_t cwd;
int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
if (err) {
@@ -2403,23 +2463,7 @@ int lfs_setattr(lfs_t *lfs, const char *path,
return err;
}
return lfs_dir_setattr(lfs, &cwd, &entry, type, buffer, size);
}
int lfs_removeattr(lfs_t *lfs, const char *path, uint8_t type) {
lfs_dir_t cwd;
int err = lfs_dir_fetch(lfs, &cwd, lfs->root);
if (err) {
return err;
}
lfs_entry_t entry;
err = lfs_dir_find(lfs, &cwd, &entry, &path);
if (err) {
return err;
}
return lfs_dir_removeattr(lfs, &cwd, &entry, type);
return lfs_dir_setattrs(lfs, &cwd, &entry, attrs, count);
}