preerase: Made REVPERTURB required to use pre-erased blocks
With REVPERTURB implemented, I think this is all we need to finish up
preerase allocations. Though not quite tested yet.
As noted when implementing lfs3_allocclaim, lfs3_allocclaim is only
half the solution for preerase allocations. If we tried to use
lfs3_allocclaim everywhere, our mdir commit path would quickly end up a
recursive mess.
This is where our ecksums kick in.
In theory, ecksums (erased-state checksums), let us detect attempted
progs. Unfortunately, in practice it's not so simple. If we tried to
detect a failed data block write, for example, it's entirely possible
the attempted write matches the erased-state exactly, making attempted
prog detection impossible. Imagine if users couldn't write all 0xffs to
a file, that'd be a weird constraint.
To work around this, we also require at least one bit flip during progs.
This ensures an ecksum failure requires a non-trivial checksum
collision.
This is where REVPERTURB comes in (and in rbyd logs, the valid bits).
---
Humorously, now that REVPERTURBs are implemented, I think the only
change required for preerased allocations is to error if REVPERTURB is
disabled.
Extra humorously, this is surprisingly tricky because REVPERTURB is a
mount flag and PREERASE a gc flag.
The solution is sort of best-effort. We error if trying to preerase
without REVPERTURB, but _don't_ error if trying to allocate when the
gbmap contains preerased blocks. This wastes the preerase cycles, but
allows disk compatibility between filesystems in different modes.
No code changes:
code stack ctx
before: 35144 2136 660
after: 35144 (+0.0%) 2136 (+0.0%) 660 (+0.0%)
code stack ctx
gbmap+np before: 38272 2144 776
gbmap+np after: 38272 (+0.0%) 2144 (+0.0%) 776 (+0.0%)
code stack ctx
gbmap+yp before: 38908 2168 796
gbmap+yp after: 38908 (+0.0%) 2168 (+0.0%) 796 (+0.0%)
This commit is contained in:
Christopher Haster
@@ -10995,11 +10995,12 @@ static lfs3_sblock_t lfs3_alloc_findfree(lfs3_t *lfs3,
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// free? erased?
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//
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// well, we can only use erased if pre-erase support is
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// enabled
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// well, we can only use erased if pre-erase and
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// revperturb is enabled
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if (tag == LFS3_TAG_BMFREE
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|| LFS3_IFDEF_PREERASE(
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tag == LFS3_TAG_BMERASED,
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tag == LFS3_TAG_BMERASED
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&& lfs3_m_isrevperturb(lfs3->flags),
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false)) {
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lfs3->gbmap.next = lfs3_min(
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(block+1) - lfs3->gbmap.window,
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@@ -15964,6 +15965,13 @@ int lfs3_mount(lfs3_t *lfs3, uint32_t flags,
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#endif
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LFS3_ASSERT(!lfs3_m_isrdonly(flags) || !lfs3_t_compact(flags));
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#endif
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// we can't use preerased blocks without revperturb, so this is
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// likely a mistake
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#if !defined(LFS3_RDONLY) \
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&& defined(LFS3_GBMAP) \
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&& !defined(LFS3_NO_PREERASE)
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LFS3_ASSERT(lfs3_m_isrevperturb(flags) || !lfs3_t_ispreerase(flags));
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#endif
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int err = lfs3_init(lfs3,
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flags & (
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@@ -16270,6 +16278,13 @@ int lfs3_format(lfs3_t *lfs3, uint32_t flags,
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| LFS3_F_COMPACT
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| LFS3_F_CKMETA
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| LFS3_F_CKDATA)) == 0);
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// we can't use preerased blocks without revperturb, so this is
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// likely a mistake
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#if !defined(LFS3_RDONLY) \
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&& defined(LFS3_GBMAP) \
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&& !defined(LFS3_NO_PREERASE)
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LFS3_ASSERT(lfs3_m_isrevperturb(flags) || !lfs3_t_ispreerase(flags));
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#endif
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int err = lfs3_init(lfs3,
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flags & (
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@@ -16733,6 +16748,14 @@ int lfs3_fs_ck(lfs3_t *lfs3, uint32_t flags) {
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LFS3_ASSERT(!lfs3_m_isrdonly(lfs3->flags)
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|| !lfs3_t_compact(flags));
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#endif
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// we can't use preerased blocks without revperturb, so this is
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// likely a mistake
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#if !defined(LFS3_RDONLY) \
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&& defined(LFS3_GBMAP) \
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&& !defined(LFS3_NO_PREERASE)
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LFS3_ASSERT(lfs3_m_isrevperturb(lfs3->flags)
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|| !lfs3_t_ispreerase(flags));
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#endif
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// set needs-ck flags, this has the side-effect of signaling ck work
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// is incomplete if we encounter an error, which is probably a good
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@@ -16748,6 +16771,7 @@ int lfs3_fs_ck(lfs3_t *lfs3, uint32_t flags) {
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// perform any pending janitorial work
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#ifdef LFS3_GC
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int lfs3_fs_gc(lfs3_t *lfs3) {
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// TODO should we actually assert on these in lfs3_init?
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// unknown gc flags?
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LFS3_ASSERT((lfs3->cfg->gc_flags & ~(
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LFS3_IFDEF_RDONLY(0, LFS3_GC_MKCONSISTENT)
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@@ -16771,6 +16795,14 @@ int lfs3_fs_gc(lfs3_t *lfs3) {
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#endif
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LFS3_ASSERT(!lfs3_m_isrdonly(lfs3->flags)
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|| !lfs3_t_compact(lfs3->cfg->gc_flags));
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// we can't use preerased blocks without revperturb, so this is
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// likely a mistake
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#if !defined(LFS3_RDONLY) \
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&& defined(LFS3_GBMAP) \
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&& !defined(LFS3_NO_PREERASE)
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LFS3_ASSERT(lfs3_m_isrevperturb(lfs3->flags)
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|| !lfs3_t_ispreerase(lfs3->cfg->gc_flags));
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#endif
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// run gc a configurable number of steps
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return lfs3_fs_gc_(lfs3, &lfs3->gc,
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@@ -17052,6 +17084,13 @@ int lfs3_trv_open(lfs3_t *lfs3, lfs3_trv_t *trv, uint32_t flags) {
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LFS3_ASSERT(!lfs3_t_ismtreeonly(flags) || !lfs3_t_islookahead(flags));
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#endif
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LFS3_ASSERT(!lfs3_t_ismtreeonly(flags) || !lfs3_t_isckdata(flags));
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// we can't use preerased blocks without revperturb, so this is
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// likely a mistake
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#if !defined(LFS3_RDONLY) \
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&& defined(LFS3_GBMAP) \
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&& !defined(LFS3_NO_PREERASE)
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LFS3_ASSERT(lfs3_m_isrevperturb(flags) || !lfs3_t_ispreerase(flags));
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#endif
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// setup traversal state
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trv->gc.t.h.flags = flags | lfs3_o_typeflags(LFS3_type_TRV);
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