From 67caa528ae08cd05e485c0ea6aea0baaf6579b06 Mon Sep 17 00:00:00 2001 From: Caleb Sander Mateos Date: Sat, 21 Jun 2025 10:28:41 -0600 Subject: ublk: fix narrowing warnings in UAPI header When a C++ file compiled with -Wc++11-narrowing includes the UAPI header linux/ublk_cmd.h, ublk_sqe_addr_to_auto_buf_reg()'s assignments of u64 values to u8, u16, and u32 fields result in compiler warnings. Add explicit casts to the intended types to avoid these warnings. Drop the unnecessary bitmasks. Reported-by: Uday Shankar Signed-off-by: Caleb Sander Mateos Fixes: 99c1e4eb6a3f ("ublk: register buffer to local io_uring with provided buf index via UBLK_F_AUTO_BUF_REG") Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/20250621162842.337452-1-csander@purestorage.com Signed-off-by: Jens Axboe --- include/uapi/linux/ublk_cmd.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h index 77d9d6af46da..c062109cb686 100644 --- a/include/uapi/linux/ublk_cmd.h +++ b/include/uapi/linux/ublk_cmd.h @@ -450,10 +450,10 @@ static inline struct ublk_auto_buf_reg ublk_sqe_addr_to_auto_buf_reg( __u64 sqe_addr) { struct ublk_auto_buf_reg reg = { - .index = sqe_addr & 0xffff, - .flags = (sqe_addr >> 16) & 0xff, - .reserved0 = (sqe_addr >> 24) & 0xff, - .reserved1 = sqe_addr >> 32, + .index = (__u16)sqe_addr, + .flags = (__u8)(sqe_addr >> 16), + .reserved0 = (__u8)(sqe_addr >> 24), + .reserved1 = (__u32)(sqe_addr >> 32), }; return reg; -- cgit v1.2.3 From 81b4d1a1d03301dcca8af5c58eded9e535f1f6ed Mon Sep 17 00:00:00 2001 From: Caleb Sander Mateos Date: Sat, 21 Jun 2025 11:10:14 -0600 Subject: ublk: update UBLK_F_SUPPORT_ZERO_COPY comment in UAPI header UBLK_F_SUPPORT_ZERO_COPY has a very old comment describing the initial idea for how zero-copy would be implemented. The actual implementation added in commit 1f6540e2aabb ("ublk: zc register/unregister bvec") uses io_uring registered buffers rather than shared memory mapping. Remove the inaccurate remarks about mapping ublk request memory into the ublk server's address space and requiring 4K block size. Replace them with a description of the current zero-copy mechanism. Signed-off-by: Caleb Sander Mateos Reviewed-by: Ming Lei Link: https://lore.kernel.org/r/20250621171015.354932-1-csander@purestorage.com Signed-off-by: Jens Axboe --- include/uapi/linux/ublk_cmd.h | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) (limited to 'include/uapi/linux') diff --git a/include/uapi/linux/ublk_cmd.h b/include/uapi/linux/ublk_cmd.h index c062109cb686..c9751bdfd937 100644 --- a/include/uapi/linux/ublk_cmd.h +++ b/include/uapi/linux/ublk_cmd.h @@ -135,8 +135,28 @@ #define UBLKSRV_IO_BUF_TOTAL_SIZE (1ULL << UBLKSRV_IO_BUF_TOTAL_BITS) /* - * zero copy requires 4k block size, and can remap ublk driver's io - * request into ublksrv's vm space + * ublk server can register data buffers for incoming I/O requests with a sparse + * io_uring buffer table. The request buffer can then be used as the data buffer + * for io_uring operations via the fixed buffer index. + * Note that the ublk server can never directly access the request data memory. + * + * To use this feature, the ublk server must first register a sparse buffer + * table on an io_uring instance. + * When an incoming ublk request is received, the ublk server submits a + * UBLK_U_IO_REGISTER_IO_BUF command to that io_uring instance. The + * ublksrv_io_cmd's q_id and tag specify the request whose buffer to register + * and addr is the index in the io_uring's buffer table to install the buffer. + * SQEs can now be submitted to the io_uring to read/write the request's buffer + * by enabling fixed buffers (e.g. using IORING_OP_{READ,WRITE}_FIXED or + * IORING_URING_CMD_FIXED) and passing the registered buffer index in buf_index. + * Once the last io_uring operation using the request's buffer has completed, + * the ublk server submits a UBLK_U_IO_UNREGISTER_IO_BUF command with q_id, tag, + * and addr again specifying the request buffer to unregister. + * The ublk request is completed when its buffer is unregistered from all + * io_uring instances and the ublk server issues UBLK_U_IO_COMMIT_AND_FETCH_REQ. + * + * Not available for UBLK_F_UNPRIVILEGED_DEV, as a ublk server can leak + * uninitialized kernel memory by not reading into the full request buffer. */ #define UBLK_F_SUPPORT_ZERO_COPY (1ULL << 0) -- cgit v1.2.3