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Added lfsr_file_resync

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lfsr_file_resync discards the current working state of a file and
reverts it to the contents on disk. It also clears the desynced flag
from files, so provides an alternative to lfsr_file_sync for when you
don't want to write to the filesystem:

  disk=A file=A        disk=A file=A
        | write B            | write B
        v                    v
  disk=A file=B        disk=A file=B
        | sync               | resync
        v                    v
  disk=B file=B        disk=A file=A

The main motivation for this is to provide a way to mark desynced
readonly files as in-sync, without putting them into a weird state where
they are "in-sync" but don't match disk.

It's also a bit safer if the file is desynced due to an error, since
errors aren't currently guaranteed to leave file data in a defined
state. Needed to resync to recover from errors avoids accidentally
syncing partial writes.

This exact behavior can also be accomplished by closing+opening the
file, but lfsr_file_resync makes it much easier without _that_ much
extra code. It may even pay for itself if you consider what code it
saves on the user's side of things.

I considered naming this lfsr_file_discard because I think it sounds
cooler, but I figured including sync in the name provides a stronger
hint that it affects the file's desync status.

---

You may think it's not possible for a readonly file to become
out-of-sync from disk, since it's, well, readonly. But it is possible
thanks to desynced files ignoring other sync broadcasts.

Consider what happens if you open a file readonly, and write+sync the
file with another file handle at the same time:

  disk=A f1=A f2=A
         | desync f2
         v
  disk=A f1=A f2=A
         | write f1=B
         v
  disk=A f1=B f2=A
         | sync f1
         v
  disk=B f1=B f2=A  <-- f2 is out-of-sync without any writes

---

This commit also changes lfsr_file_sync/flush to assert if the file is
readonly. Previously we allowed lfsr_file_sync to be called on readonly
files if it would be a noop, but lfsr_file_resync makes this
unnecessary.

More code means more code, but I think it is well worth it for the
additional flexibility:

           code          stack
  before: 36412           2616
  after:  36748 (+0.9%)   2616 (+0.0%)
This commit is contained in:
Christopher Haster
2024-08-20 18:33:38 -05:00
parent da9ac39c88
commit ed96e304de
3 changed files with 1471 additions and 160 deletions
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lfs.c
+121 -30
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@@ -11127,15 +11127,15 @@ int lfsr_file_opencfg(lfs_t *lfs, lfsr_file_t *file,
}
// setup file state
file->cfg = cfg;
file->o.o.flags = lfsr_o_settype(flags, LFS_TYPE_REG)
// mounted with LFS_M_FLUSH/SYNC? implies LFS_O_FLUSH/SYNC
| (lfs->flags & (LFS_M_FLUSH | LFS_M_SYNC));
file->cfg = cfg;
// default data state
file->o.bshrub = LFSR_BSHRUB_BNULL();
file->pos = 0;
file->eblock = 0;
file->eoff = -1;
// default data state
file->o.bshrub = LFSR_BSHRUB_BNULL();
// lookup our parent
lfsr_tag_t tag;
@@ -11202,7 +11202,7 @@ int lfsr_file_opencfg(lfs_t *lfs, lfsr_file_t *file,
// if we're truncating don't bother to read any state, we're
// just going to truncate after all
if (!lfsr_o_istrunc(flags)) {
// read any inlined state
// lookup the file struct, if there is one
lfsr_tag_t tag;
lfsr_data_t data;
err = lfsr_mdir_lookupnext(lfs, &file->o.o.mdir, LFSR_TAG_DATA,
@@ -11259,9 +11259,10 @@ int lfsr_file_opencfg(lfs_t *lfs, lfsr_file_t *file,
file->buffer.size = 0;
// if our file is small, try to keep the whole thing in our buffer
if (lfsr_bshrub_size(&file->o.bshrub) <= lfsr_file_inlinesize(lfs, file)) {
lfs_size_t size = lfsr_bshrub_size(&file->o.bshrub);
if (size <= lfsr_file_inlinesize(lfs, file)) {
lfs_ssize_t d = lfsr_file_read_(lfs, file,
0, file->buffer.buffer, lfsr_bshrub_size(&file->o.bshrub));
0, file->buffer.buffer, size);
if (d < 0) {
err = d;
goto failed;
@@ -11269,9 +11270,9 @@ int lfsr_file_opencfg(lfs_t *lfs, lfsr_file_t *file,
// small files remain perpetually unflushed
file->o.o.flags |= LFS_O_UNFLUSH;
file->buffer.pos = 0;
file->buffer.size = lfsr_bshrub_size(&file->o.bshrub);
file->o.bshrub = LFSR_BSHRUB_BNULL();
file->buffer.pos = 0;
file->buffer.size = size;
}
// check metadata/data for errors?
@@ -12561,10 +12562,8 @@ failed:;
int lfsr_file_flush(lfs_t *lfs, lfsr_file_t *file) {
LFS_ASSERT(lfsr_omdir_isopen(lfs, &file->o.o));
// readonly files should do nothing
LFS_ASSERT(!lfsr_o_isrdonly(file->o.o.flags)
|| !lfsr_o_isunflush(file->o.o.flags)
|| lfsr_file_size_(file) <= lfsr_file_inlinesize(lfs, file));
// can't write to readonly files
LFS_ASSERT(!lfsr_o_isrdonly(file->o.o.flags));
// do nothing if our file is already flushed
if (!lfsr_o_isunflush(file->o.o.flags)) {
@@ -12609,6 +12608,10 @@ failed:;
int lfsr_file_sync(lfs_t *lfs, lfsr_file_t *file) {
LFS_ASSERT(lfsr_omdir_isopen(lfs, &file->o.o));
// can't write to readonly files, if you want to resync call
// lfsr_file_resync
LFS_ASSERT(!lfsr_o_isrdonly(file->o.o.flags));
// removed? we can't sync
int err;
if (lfsr_o_iszombie(file->o.o.flags)) {
@@ -12648,23 +12651,8 @@ int lfsr_file_sync(lfs_t *lfs, lfsr_file_t *file) {
LFS_ASSERT(!lfsr_o_isorphan(file->o.o.flags)
|| lfsr_o_isunsync(file->o.o.flags));
// don't write to disk if our disk is already in-sync
// don't write to disk if already in-sync
if (lfsr_o_isunsync(file->o.o.flags)) {
// readonly files should do nothing
//
// but readonly files _can_ end up unsynced, in the roundabout
// case where:
//
// 1. a file is opened rdonly + desync
// 2. the same file is opened and written to
// 3. we try to sync our original file handle
//
// the best thing we can do in this case is return an error
if (lfsr_o_isrdonly(file->o.o.flags)) {
err = LFS_ERR_INVAL;
goto failed;
}
// commit any changes to our file's metadata
lfsr_attr_t attrs[2];
lfs_size_t attr_count = 0;
@@ -12782,10 +12770,113 @@ int lfsr_file_desync(lfs_t *lfs, lfsr_file_t *file) {
(void)lfs;
LFS_ASSERT(lfsr_omdir_isopen(lfs, &file->o.o));
// mark as desynced
file->o.o.flags |= LFS_O_DESYNC;
return 0;
}
int lfsr_file_resync(lfs_t *lfs, lfsr_file_t *file) {
LFS_ASSERT(lfsr_omdir_isopen(lfs, &file->o.o));
// removed? we can't resync
int err;
if (lfsr_o_iszombie(file->o.o.flags)) {
err = LFS_ERR_NOENT;
goto failed;
}
// do nothing if already in-sync
if (lfsr_o_isunsync(file->o.o.flags)) {
// default data state
file->o.bshrub_ = LFSR_BSHRUB_BNULL();
// don't bother reading disk if we're an orphan
if (!lfsr_o_isorphan(file->o.o.flags)) {
// lookup the file struct, if there is one
lfsr_tag_t tag;
lfsr_data_t data;
err = lfsr_mdir_lookupnext(lfs, &file->o.o.mdir, LFSR_TAG_DATA,
&tag, &data);
if (err && err != LFS_ERR_NOENT) {
goto failed;
}
// note many of these functions leave bshrub undefined if
// there is an error, so we first read into the staging
// bshrub
// may be a sprout (simple inlined data)
if (err != LFS_ERR_NOENT && tag == LFSR_TAG_DATA) {
file->o.bshrub_.u.bsprout = data;
// or a direct block
} else if (err != LFS_ERR_NOENT && tag == LFSR_TAG_BLOCK) {
err = lfsr_data_readbptr(lfs, &data,
&file->o.bshrub_.u.bptr);
if (err) {
goto failed;
}
// or a bshrub (inlined btree)
} else if (err != LFS_ERR_NOENT && tag == LFSR_TAG_BSHRUB) {
err = lfsr_data_readshrub(lfs, &data, &file->o.o.mdir,
&file->o.bshrub_.u.bshrub);
if (err) {
goto failed;
}
// or a btree
} else if (err != LFS_ERR_NOENT && tag == LFSR_TAG_BTREE) {
err = lfsr_data_fetchbtree(lfs, &data,
&file->o.bshrub_.u.btree);
if (err) {
goto failed;
}
}
}
// mark as flushed and synced if we're not an orphan
file->o.o.flags &= ~(
LFS_O_UNFLUSH
| ((!lfsr_o_isorphan(file->o.o.flags))
? LFS_O_UNSYNC
: 0));
// update the bshrub
file->o.bshrub = file->o.bshrub_;
// discard the current buffer
file->buffer.pos = 0;
file->buffer.size = 0;
// if our file is small, try to keep the whole thing in our buffer
//
// if this fails we may end up with corrupt data, but that's ok, we
// just can't end up with corrupt metadata
lfs_size_t size = lfsr_bshrub_size(&file->o.bshrub);
if (size <= lfsr_file_inlinesize(lfs, file)) {
lfs_ssize_t d = lfsr_file_read_(lfs, file,
0, file->buffer.buffer, size);
if (d < 0) {
err = d;
goto failed;
}
// small files remain perpetually unflushed
file->o.o.flags |= LFS_O_UNFLUSH;
file->o.bshrub = LFSR_BSHRUB_BNULL();
file->buffer.pos = 0;
file->buffer.size = size;
}
}
// mark as resynced
file->o.o.flags &= ~LFS_O_DESYNC;
return 0;
failed:;
file->o.o.flags |= LFS_O_DESYNC;
return err;
}
// other file operations
lfs_soff_t lfsr_file_seek(lfs_t *lfs, lfsr_file_t *file,
@@ -12897,9 +12988,9 @@ int lfsr_file_truncate(lfs_t *lfs, lfsr_file_t *file, lfs_off_t size_) {
// small files remain perpetually unflushed
file->o.o.flags |= LFS_O_UNFLUSH;
file->o.bshrub = LFSR_BSHRUB_BNULL();
file->buffer.pos = 0;
file->buffer.size = size_;
file->o.bshrub = LFSR_BSHRUB_BNULL();
// truncate our file normally
} else {
@@ -13019,9 +13110,9 @@ int lfsr_file_fruncate(lfs_t *lfs, lfsr_file_t *file, lfs_off_t size_) {
// small files remain perpetually unflushed
file->o.o.flags |= LFS_O_UNFLUSH;
file->o.bshrub = LFSR_BSHRUB_BNULL();
file->buffer.pos = 0;
file->buffer.size = size_;
file->o.bshrub = LFSR_BSHRUB_BNULL();
// fruncate our file normally
} else {