add descriptor table for mapping fds to handles #464
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This introduces `descriptor_table.h` and `descriptor_table.c`, providing a global hashtable for tracking `wasi-libc`-managed file descriptors. WASI Preview 2 has no notion of file descriptors and instead uses unforgeable resource handles. Moreover, there's not necessarily a one-to-one correspondence between POSIX file descriptors and resource handles (e.g. a TCP connection may require separate handles for reading, writing, and polling the same connection). We use this table to map each POSIX descriptor to a set of one or more handles and any extra state which libc needs to track. Note that we've added `descriptor_table.h` to the libc-bottom-half/headers/public/wasi directory, making it part of the public API. The intention is to give applications access to the mapping, enabling them to convert descriptors to handles and vice-versa should they need to interoperate with both libc and WASI directly. Co-authored-by: Dave Bakker <[email protected]> Signed-off-by: Joel Dice <[email protected]>
yamt
reviewed
Jan 23, 2024
sbc100
reviewed
Feb 12, 2024
The C standard doesn't allow empty structs. Clang doesn't currently complain, but we might as well stick to the spec in case it becomes more strict in the future. Signed-off-by: Joel Dice <[email protected]>
We're not yet ready to commit to making this API public, so we'll make it private for now. I've also expanded a comment in descriptor_table.c to explain the current ABI for resource handles. Signed-off-by: Joel Dice <[email protected]>
Signed-off-by: Joel Dice <[email protected]>
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This introduces
descriptor_table.handdescriptor_table.c, providing a global hashtable for trackingwasi-libc-managed file descriptors.WASI Preview 2 has no notion of file descriptors and instead uses unforgeable resource handles (which are currently represented as integers at the ABI level, used as indices into per-component tables managed by the host). Moreover, there's not necessarily a one-to-one correspondence between POSIX file descriptors and resource handles (e.g. a TCP connection may require separate handles for reading, writing, and polling the same connection). We use this table to map each POSIX descriptor to a set of one or more handles and any extra state which libc needs to track.
Note that we've added
descriptor_table.hto thelibc-bottom-half/headers/public/wasi directory, making it part of the public API. The intention is to give applications access to the mapping, enabling them to convert descriptors to handles and vice-versa should they need to interoperate with both libc and WASI directly.