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Nov 11, 2026
| // The result of a zerocopy notification is a set of flags, not an | ||
| // errno: with `IORING_SEND_ZC_REPORT_USAGE` the kernel sets | ||
| // `IORING_NOTIF_USAGE_ZC_COPIED` (`1 << 31`) when the data was copied. | ||
| Ok(result as u32 as usize) |
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Should clear the flag instead of a conversion.
| //! A zerocopy notification reports its usage in the sign bit of `res`, which | ||
| //! must not be read as an errno. | ||
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| #![cfg(all(io_uring, not(fusion)))] |
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The
resof a zerocopy notification isn't an errno. When the send setsIORING_SEND_ZC_REPORT_USAGE, the kernel putsIORING_NOTIF_USAGE_ZC_COPIED(1 << 31) there if it copied the data (uapi, v6.2, notif.c).create_resultreads it as a negative errno and negates it (iour/mod.rs).-i32::MINoverflows, so a debug build panics and a release build returns anio::Errorwith a garbage code.compio's own
SendZcops don't set the flag, but anyOpCodethat setszc_flagsto get the usage report runs into this.create_resultnow checksIORING_CQE_F_NOTIFfirst and returns the notification'sresasu32.Extra::is_notificationdocuments what that value holds.The new test sends over loopback with
REPORT_USAGE, where the kernel always copies, and checks that the notification reports the copy. On master it panics with "attempt to negate with overflow"; with this change it passes on Linux 6.18. It skips on kernels that reject the flag.