Io uring

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==Rings==

Central to every uring are two ringbuffers holding CQEs (Completion Queue Entries) and ~~SQEs~~ (Submission Queue Entries) (as best I can tell, this terminology was used in the NVMe specification, and before that on the IBM AS400). SQEs roughly correspond to a single system call: they are tagged with an operation type, and filled in with the values that would traditionally be supplied as arguments to the appropriate function. Userspace is provided references to SQEs on the SQE ring, filled in, and submitted. Submission operates up through a specified SQE, and thus all SQEs before it in the ring must also be ready to go. The kernel places results in the CQE ring. These rings are shared between kernel- and userspace. The rings must be distinct unless the kernel specifies the <tt>IORING_FEAT_SINGLE_MMAP</tt> feature (see below). Note that SQEs are allocated externally to the SQ descriptor ring.

Central to every uring are two ringbuffers holding CQEs (Completion Queue Entries) and SQE (Submission Queue Entries) descriptors (as best I can tell, this terminology was used in the NVMe specification, and before that on the IBM AS400). SQEs roughly correspond to a single system call: they are tagged with an operation type, and filled in with the values that would traditionally be supplied as arguments to the appropriate function. Userspace is provided references to SQEs on the SQE ring, filled in, and submitted. Submission operates up through a specified SQE, and thus all SQEs before it in the ring must also be ready to go. The kernel places results in the CQE ring. These rings are shared between kernel- and userspace. The rings must be distinct unless the kernel specifies the <tt>IORING_FEAT_SINGLE_MMAP</tt> feature (see below). Note that SQEs are allocated externally to the SQ descriptor ring.

It is possible for a single submission to result in multiple completions (e.g. <tt>io_uring_prep_multishot_accept(3)</tt>); this is known as ''multishot''.

Io uring: Difference between revisions

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 ==Rings==
-Central to every uring are two ringbuffers holding CQEs (Completion Queue Entries) and SQEs (Submission Queue Entries) (as best I can tell, this terminology was used in the NVMe specification, and before that on the IBM AS400). SQEs roughly correspond to a single system call: they are tagged with an operation type, and filled in with the values that would traditionally be supplied as arguments to the appropriate function. Userspace is provided references to SQEs on the SQE ring, filled in, and submitted. Submission operates up through a specified SQE, and thus all SQEs before it in the ring must also be ready to go. The kernel places results in the CQE ring. These rings are shared between kernel- and userspace. The rings must be distinct unless the kernel specifies the <tt>IORING_FEAT_SINGLE_MMAP</tt> feature (see below). Note that SQEs are allocated externally to the SQ descriptor ring.
+Central to every uring are two ringbuffers holding CQEs (Completion Queue Entries) and SQE (Submission Queue Entries) descriptors (as best I can tell, this terminology was used in the NVMe specification, and before that on the IBM AS400). SQEs roughly correspond to a single system call: they are tagged with an operation type, and filled in with the values that would traditionally be supplied as arguments to the appropriate function. Userspace is provided references to SQEs on the SQE ring, filled in, and submitted. Submission operates up through a specified SQE, and thus all SQEs before it in the ring must also be ready to go. The kernel places results in the CQE ring. These rings are shared between kernel- and userspace. The rings must be distinct unless the kernel specifies the <tt>IORING_FEAT_SINGLE_MMAP</tt> feature (see below). Note that SQEs are allocated externally to the SQ descriptor ring.
 It is possible for a single submission to result in multiple completions (e.g. <tt>io_uring_prep_multishot_accept(3)</tt>); this is known as ''multishot''.