io_uring: allow use of offset == -1 to mean file position

This behaves like preadv2/pwritev2 with offset == -1, it'll use (and update) the current file position. This obviously comes with the caveat that if the application has multiple read/writes in flight, then the end result will not be as expected. This is similar to threads sharing a file descriptor and doing IO using the current file position. Since this feature isn't easily detectable by doing a read or write, add a feature flags, IORING_FEAT_RW_CUR_POS, to allow applications to detect presence of this feature.

Jens Axboe committed 6 years ago

Commit ba042911 parent 3a6820f2 files · +11 −1Browse files

Showing the changes to include/uapi/linux (1 of 2 files). Show all

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include/uapi/linux/io_uring.h+1−0

@@ -174,6 +174,7 @@ struct io_uring_params { · 173 unmodified lines
174	174	#define IORING_FEAT_SINGLE_MMAP (1U << 0)
175	175	#define IORING_FEAT_NODROP (1U << 1)
176	176	#define IORING_FEAT_SUBMIT_STABLE (1U << 2)
	177	+#define IORING_FEAT_RW_CUR_POS (1U << 3)
177	178
178	179	/*
179	180	* io_uring_register(2) opcodes and arguments