GitLab

Allow mojo_utils in wilco_dtc_supportd to use ScopedAllowBlocking's
private ctor.

GetStringPieceFromMojoHandle() runs in the browser process and has
DCHECK errors. This is because GetStringPieceFromMojoHandle() uses
base::file::Fstat() that is marked with ScopedBlockingCall.

Background: Referring to the discussion in
https://chromium-review.googlesource.com/c/chromium/src/+/2042611, the
ideal solution to this problem is to upgrade mojo library in chromeos
(mojo library in chromeos is 1-2 years older than chrome). Doing that,
the new shmem builtin types can be used and we won't need to get the
handle's length in the first place.

The problem with that is upgrade will take time. So, as a temporary
solution, allow mojo_utils in wilco_dtc_supportd to use
ScopedAllowBlocking's private ctor by making the class friend with
ScopedAllowBlocking.

The justification as per alexilin@ is that: Fstat() shouldn't be
blocking for shared memory descriptors (i.e. mojo handle). Fstat() will
read tmpfs metadata that is always stored in RAM. That metadata is
never swapped to disk since it's part of kernel-allocated memory that
is never swapped out.

Bug: 1055467,b:146119375
TEST=building and running unittests

Change-Id: Iba688b7f311c07b051687a1f619b594475892178
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2070160
Commit-Queue: Mahmoud Gawad <mgawad@google.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Oleh Lamzin <lamzin@google.com>
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746317}