Commit 8450b76918 (package/pkg-cargo: move CARGO_HOME into DL_DIR)
allowed for a shared cargo cache of crates. Internally, cargo is
supposed to lock themselves when accessing that cache, and that commit
even had some research in that area, pointing at [0] for complaints
about too-coarse the lock, so it was deemed safe to have a shared cargo
home.
However, in practice, the locking as implemented by cargo, fails to
properly protect the concurrent accesses to the crates cache, with random
failures that manifest themselves like so:
Blocking waiting for file lock on package cache
Blocking waiting for file lock on package cache
Downloading crates ...
error: failed to sync
Caused by:
failed to download packages
Caused by:
failed to download `autocfg v1.1.0`
Caused by:
unable to get packages from source
Caused by:
failed to unpack package `autocfg v1.1.0`
Caused by:
failed to unpack entry at `autocfg-1.1.0/src/tests.rs`
Caused by:
No such file or directory (os error 2) while canonicalizing [...]
with the last few errors sometime being:
Caused by:
failed to parse manifest at `[...]/aho-corasick-0.7.18/Cargo.toml`
Caused by:
can't find library `aho_corasick`, rename file to `src/lib.rs` or specify lib.path
So, as we do not systematically use our own cargo build (we can use a
pre-built one with host-rust-bin), we can't patch cargo (even if we knew
what to do!).
Instead, we implement a lock ourselves, by wrapping the call to "cargo
vendor" with a flock(1) on cargo home.
Note: the download wrapper is already flock-ed, but it is a per-package
lock, so it does not prevent different packages from being downloaded in
parallel; if those packages need cargo vendoring, that will not be
protected by the flock on the dl wrapper. So we really do need a flock
on cargo home.
[0] https://github.com/rust-lang/cargo/issues/6930
Fixes: 8450b76918
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Moritz Bitsch <moritz@h6t.eu>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
fbddd12601