Summary: Boot sequence around apexd is changed to make it possible for
pre-apexd processes to use libraries from APEXes. They no longer need to
wait for the apexd to finish activating APEXes, which again can be
done only after /data/ is mounted. This improves overall boot
performance.
Detail: This change fixes the problem that processes that are started
before apexd (so called pre-apexd processes) can't access libraries
that are provided only by the APEXes but are not found in the system
partition (e.g. libdexfile_external.so, etc.). Main idea is to activate
system APEXes (/system/apex/*.apex) before /data is mounted and then
activate the updated APEXes (/data/apex/*.apex) after the /data mount.
Detailed boot sequence is as follows.
1) init prepares the bootstrap and default mount namespaces. A tmpfs is
mounted on /apex and the propagation type of the mountpoint is set to
private.
2) before any other process is started, apexd is started in bootstrap
mode. When executed in the mode, apexd only activates APEXes under
/system/apex. Note that APEXes activated in this phase are mounted in
the bootstrap mount namespace only.
3) other pre-apexd processes are started. They are in the bootstrap
mount namespace and thus are provided with the libraries from the system
APEXes.
4) /data is mounted. init switches into the default mount namespace and
starts apexd as a daemon as usual.
5) apexd scans both /data/apex and /system/apex, and activate latest
APEXes from the directories. Note that APEXes activated in this phase
are mounted in the default namespaces only and thus are not visible to
the pre-apexd processes.
Bug: 125549215
Test: m; device boots
Change-Id: I21c60d0ebe188fa4f24d6e6861f85ca204843069
This CL fixes the design problem of the previous mechanism for providing
the bootstrap bionic and the runtime bionic to the same path.
Previously, bootstrap bionic was self-bind-mounted; i.e.
/system/bin/libc.so is bind-mounted to itself. And the runtime bionic
was bind-mounted on top of the bootstrap bionic. This has not only caused
problems like `adb sync` not working(b/122737045), but also is quite
difficult to understand due to the double-and-self mounting.
This is the new design:
Most importantly, these four are all distinct:
1) bootstrap bionic (/system/lib/bootstrap/libc.so)
2) runtime bionic (/apex/com.android.runtime/lib/bionic/libc.so)
3) mount point for 1) and 2) (/bionic/lib/libc.so)
4) symlink for 3) (/system/lib/libc.so -> /bionic/lib/libc.so)
Inside the mount namespace of the pre-apexd processes, 1) is
bind-mounted to 3). Likewise, inside the mount namespace of the
post-apexd processes, 2) is bind-mounted to 3). In other words, there is
no self-mount, and no double-mount.
Another change is that mount points are under /bionic and the legacy
paths become symlinks to the mount points. This is to make sure that
there is no bind mounts under /system, which is breaking some apps.
Finally, code for creating mount namespaces, mounting bionic, etc are
refactored to mount_namespace.cpp
Bug: 120266448
Bug: 123275379
Test: m, device boots, adb sync/push/pull works,
especially with following paths:
/bionic/lib64/libc.so
/bionic/bin/linker64
/system/lib64/bootstrap/libc.so
/system/bin/bootstrap/linker64
Change-Id: Icdfbdcc1efca540ac854d4df79e07ee61fca559f
