[v0.10] cache: add fallback for snapshotID

[tonistiigi]

fix for moby/moby#44943

In older BuildKit versions, snapshotID was not always set if the record was not created with GetByBlob method. Old code defaulted to cache record ID in that case, but that broke with the metadata interface refactor.

Regression for this fallback is in:
before: a9f1980#diff-e4a99c1c50054f36891bbe03da3784b5d2d4ca6b279ff32c7999d3ac5db48dc7L81

after: a9f1980#diff-e4a99c1c50054f36891bbe03da3784b5d2d4ca6b279ff32c7999d3ac5db48dc7R250

It doesn't appear in current versions (at least) because snapshotID is explicitly set in finalize/commit a9f1980#diff-94cb4012b7ea73b110c7ac219d52793e11b96d9141c3ad631603f34a7fc9289aR917

finalize:

commit:

@neersighted @thaJeztah @sipsma

Signed-off-by: Tonis Tiigi tonistiigi@gmail.com

[neersighted]

Two quick questions as someone who is naive to BuildKit:

• Does this fix also need to go in v0.11, as an old cache could still be loaded?
• Does it make more sense to encapsulate this logic inside md.GetString()?

[tonistiigi]

Does this fix also need to go in v0.11, as an old cache could still be loaded?

Yes. If we want cache from 20.10 to not break Moby master.

Does it make more sense to encapsulate this logic inside md.GetString()?

No, this is specific fallback only for the snapshotID value.

[thaJeztah]

Any idea what this failiure is / was ? Looks weird https://github.com/moby/buildkit/actions/runs/4120008980/jobs/7114304809

 > [linux/amd64->riscv64 runc 3/3] RUN --mount=from=runc-src,src=/usr/src/runc,target=. --mount=target=/root/.cache,type=cache   CGO_ENABLED=1 xx-go build -mod=vendor -ldflags '-extldflags -static' -tags 'apparmor seccomp netgo cgo static_build osusergo' -o /usr/bin/runc ./ &&   xx-verify --static /usr/bin/runc:
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x006.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x007.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x008.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x009.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x010.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: -march=rv64i2p1_m2p0_a2p1_f2p2_d2p2_c2p0_zicsr2p0_zifencei2p0_zmmul1p0: unknown z ISA extension `zmmul'
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file /riscv64-alpine-linux-musl//usr/lib/gcc/riscv64-alpine-linux-musl/12.2.1/crtendS.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: -march=rv64i2p1_m2p0_a2p1_f2p2_d2p2_c2p0_zicsr2p0_zifencei2p0_zmmul1p0: unknown z ISA extension `zmmul'
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file /riscv64-alpine-linux-musl//usr/lib/gcc/riscv64-alpine-linux-musl/12.2.1/crtn.o
#60 106.3 clang-12: error: linker command failed with exit code 1 (use -v to see invocation)
------
Dockerfile:47
--------------------
  46 |       [ "$(xx-info arch)" != "ppc64le" ] || XX_CC_PREFER_LINKER=ld xx-clang --setup-target-triple
  47 | >>> RUN --mount=from=runc-src,src=/usr/src/runc,target=. --mount=target=/root/.cache,type=cache \
  48 | >>>   CGO_ENABLED=1 xx-go build -mod=vendor -ldflags '-extldflags -static' -tags 'apparmor seccomp netgo cgo static_build osusergo' -o /usr/bin/runc ./ && \
  49 | >>>   xx-verify --static /usr/bin/runc
  50 |     

[crazy-max]

Any idea what this failiure is / was ? Looks weird https://github.com/moby/buildkit/actions/runs/4120008980/jobs/7114304809

 > [linux/amd64->riscv64 runc 3/3] RUN --mount=from=runc-src,src=/usr/src/runc,target=. --mount=target=/root/.cache,type=cache   CGO_ENABLED=1 xx-go build -mod=vendor -ldflags '-extldflags -static' -tags 'apparmor seccomp netgo cgo static_build osusergo' -o /usr/bin/runc ./ &&   xx-verify --static /usr/bin/runc:
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x006.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x007.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x008.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x009.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file $WORK/b192/_x010.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: -march=rv64i2p1_m2p0_a2p1_f2p2_d2p2_c2p0_zicsr2p0_zifencei2p0_zmmul1p0: unknown z ISA extension `zmmul'
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file /riscv64-alpine-linux-musl//usr/lib/gcc/riscv64-alpine-linux-musl/12.2.1/crtendS.o
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: -march=rv64i2p1_m2p0_a2p1_f2p2_d2p2_c2p0_zicsr2p0_zifencei2p0_zmmul1p0: unknown z ISA extension `zmmul'
#60 106.3 /usr/bin/riscv64-alpine-linux-musl-ld: failed to merge target specific data of file /riscv64-alpine-linux-musl//usr/lib/gcc/riscv64-alpine-linux-musl/12.2.1/crtn.o
#60 106.3 clang-12: error: linker command failed with exit code 1 (use -v to see invocation)
------
Dockerfile:47
--------------------
  46 |       [ "$(xx-info arch)" != "ppc64le" ] || XX_CC_PREFER_LINKER=ld xx-clang --setup-target-triple
  47 | >>> RUN --mount=from=runc-src,src=/usr/src/runc,target=. --mount=target=/root/.cache,type=cache \
  48 | >>>   CGO_ENABLED=1 xx-go build -mod=vendor -ldflags '-extldflags -static' -tags 'apparmor seccomp netgo cgo static_build osusergo' -o /usr/bin/runc ./ && \
  49 | >>>   xx-verify --static /usr/bin/runc
  50 |     

Yes catch this one in #3587 (review). I'm not sure yet but best guess is this could be linked to libseccomp package from alpine repo:

buildkit/Dockerfile

Line 45 in b8fdb4b

RUN set -e; xx-apk add musl-dev gcc libseccomp-dev libseccomp-static; \

[neersighted]

Can we tag a release for this fix before we re-vendor in Moby?

[neersighted]

Also, just thinking about this change/bug a bit more:

• Can we create a regression test that generates a cache without a metadata.ID() to guard against this in the future?
• It feels like a code smell that an empty string was allowed to silently break things -- should functions up the call chain be somehow validating that they are not passed an empty layer ID to load (or whatever the abstraction is)?

[tonistiigi]

Can we create a regression test that generates a cache without a metadata.ID() to guard against this in the future?

We do not have any version upgrade tests atm. that could have caught this.

It feels like a code smell that an empty string was allowed to silently break things -- should functions up the call chain be somehow validating that they are not passed an empty layer ID to load (or whatever the abstraction is)?

Sure, but the old code was pretty strict that this variable could never be empty. A regression that broke that seems to have been an oversight during a big refactor, and there was no intention to change the behavior behind it. This way, any time we pass a variable to a function, we would need to do a if var == "" check if we would want to check for any bug that could be setting var="" in some other function. A language that distinguishes empty values in the type system would have caught this bug.

[neersighted]

If there's not an explicit way to catch it without nil-guarding, fair enough. ZSTs are certainly the thing that makes the most sense here, but we don't work with a language that has such a rich type system 😆

It seems like the best thing to add is a regression for this case/upgrade tests with a gold corpus in general, that way we can guard against future similar regressions.

[neersighted]

Related: #3605