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rustbot added O-hermit

Operating System: Hermit

O-unix

Operating system: Unix-like

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Status: Awaiting review from the assignee but also interested parties.

T-libs

Relevant to the library team, which will review and decide on the PR/issue.

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Mar 24, 2025

rustbot added the T-libs-api

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Mar 24, 2025

readv and writev are constrained by a platform-specific upper bound on the number of buffers which can be passed. Currently, read_vectored and write_vectored implementations simply truncate to this limit when larger. However, when the only non-empty buffers are at indices above this limit, they will erroneously return Ok(0).

Instead, slice the buffers starting at the first non-empty buffer. This trades a conditional move for a branch, so it's barely a penalty in the common case.

The new method limit_slices on IoSlice and IoSliceMut may be generally useful to users like advance_slices is, but I have left it as pub(crate) for now.

POSIX requires at least one buffer passed to readv and writev, but we allow the user to pass an empty slice of buffers. In this case, return a zero-length read or write.