With IORING_REGISTER_USE_REGISTERED_RING, an application can register the ring fd and use it via registered index rather than installed fd. This allows using a registered ring for everything *except* the initial mmap. With IORING_SETUP_NO_MMAP, io_uring_setup uses buffers allocated by the user, rather than requiring a subsequent mmap. The combination of the two allows a user to operate *entirely* via a registered ring fd, making it unnecessary to ever install the fd in the first place. So, add a flag IORING_SETUP_REGISTERED_FD_ONLY to make io_uring_setup register the fd and return a registered index, without installing the fd. This allows an application to avoid touching the fd table at all, and allows a library to never even momentarily install a file descriptor. This splits out an io_ring_add_registered_file helper from io_ring_add_registered_fd, for use by io_uring_setup.
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| @@ -178,6 +178,13 @@ enum { · 177 unmodified lines | ||
| 178 | 178 | */ |
| 179 | 179 | #define IORING_SETUP_NO_MMAP (1U << 14) |
| 180 | 180 | |
| 181 | +/* | |
| 182 | + * Register the ring fd in itself for use with | |
| 183 | + * IORING_REGISTER_USE_REGISTERED_RING; return a registered fd index rather | |
| 184 | + * than an fd. | |
| 185 | + */ | |
| 186 | +#define IORING_SETUP_REGISTERED_FD_ONLY (1U << 15) | |
| 187 | + | |
| 181 | 188 | enum io_uring_op { |
| 182 | 189 | IORING_OP_NOP, |
| 183 | 190 | IORING_OP_READV, |