Convenient no-panic API for just waiting on notifications #1715
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These comments by 2020-me didn't super make sense to 2024-me, so I have rewritten them to hopefully be a little more clear and reveal some context that was previously implicit.
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hawkw
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| // We're not using the extract_new_generation function here because | ||
| // that has a failure code path for cases where the code is not a | ||
| // dead code. In this case, sys_recv is defined as being _only_ | ||
| // capable of returning a dead code -- otherwise we have a serious | ||
| // kernel bug. So to avoid the introduction of a panic that can't | ||
| // trigger, we will do this manually: |
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This comment is great, thanks for adding it!
This is an alternate API for accessing the common "receive only kernel notifications" pattern. That specific use of the sys_recv syscall is defined as not being able to fail. Different users have handled that in different ways -- some panic, some ignore the result. The latter embeds the assumption of that behavior in many different places in the codebase, a pattern I'm trying to keep an eye on. This change adds a new sys_recv_notification userlib function that bundles up this common pattern. Because of its central placement in userlib, it seems like a more appropriate place to encode the assumption about the syscall not failing, and so I've done that, using unreachable_unchecked to explain it to the compiler. This removes a panic site from every notification-wait in programs that were previously using unwrap or unwrap_lite.
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This is an alternate API for accessing the common "receive only kernel
notifications" pattern. That specific use of the sys_recv syscall is
defined as not being able to fail. Different users have handled that in
different ways -- some panic, some ignore the result. The latter embeds
the assumption of that behavior in many different places in the
codebase, a pattern I'm trying to keep an eye on.
This change adds a new sys_recv_notification userlib function that
bundles up this common pattern. Because of its central placement in
userlib, it seems like a more appropriate place to encode the assumption
about the syscall not failing, and so I've done that, using
unreachable_unchecked to explain it to the compiler.
This removes a panic site from every notification-wait in programs that
were previously using unwrap or unwrap_lite.