runsc/boot: add per-mount directfs opt-out#13099
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runsc/boot: add per-mount directfs opt-out#13099shayonj wants to merge 1 commit intogoogle:masterfrom
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The --directfs flag is global: when enabled, every gofer mount in the
sandbox includes the "directfs" option, which causes the sentry to
require a host FD for the mount root from the gofer's Mount RPC reply.
Custom gofer servers that back virtual or network-backed filesystems
cannot donate such an FD and must currently disable --directfs globally,
losing the directfs performance benefit on every other mount.
Add a new "directfs" key to the dev.gvisor.spec.mount.<NAME>.*
mount annotation. When set to "off", the sentry suppresses the directfs
mount option for that mount only, regardless of the global --directfs
setting. The default ("on" or unset) preserves current behavior.
Plumbing reuses the existing MountHint mechanism in runsc/boot. The
rootfs path passes no mount hint to goferMountData and is therefore
unaffected; the annotation only applies to submounts that are matched by
mount source.
Tests cover annotation parsing and goferMountData behavior across the
global directfs and per-mount opt-out combinations.
Fixes google#13098
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The --directfs flag is global: when enabled, every gofer mount in the
sandbox includes the "directfs" option, which causes the sentry to
require a host FD for the mount root from the gofer's Mount RPC reply.
Custom gofer servers that back virtual or network-backed filesystems
(e.g. a blob-store-backed volume gofer) cannot donate such an FD and
must currently disable --directfs globally to coexist with the stock
gofer, losing the directfs performance benefit on every other mount.
This PR adds a new "directfs" key to the
dev.gvisor.spec.mount..* mount annotation. When set to "off", the
sentry suppresses the directfs mount option for that mount only,
regardless of the global --directfs setting. The default ("on" or
unset) preserves current behavior.
Plumbing reuses the existing MountHint mechanism in runsc/boot. The
rootfs path passes no mount hint to goferMountData and is therefore
unaffected and the annotation only applies to submounts that are matched by
mount source. The opt-out is applied on the sentry mount-data path, so
a stock gofer may still donate a mount-root FD when --directfs is
enabled globally, but the sentry will not use directfs for an opted-out
mount.
Tests cover annotation parsing, including invalid values that are
ignored without dropping the rest of the hint, and goferMountData
behavior across the global directfs and per-mount opt-out combinations.
This does not change checkpoint or restore mechanics directly, but it
can reduce first-exec latency after restore in mixed custom-gofer
sandboxes. A custom mount can stay on the LisaFS RPC path while rootfs
and ordinary bind mounts continue to use directfs for binary, library,
and cache reads.
Fixes #13098.