structiov_iter { /* * Bit 0 is the read/write bit, set if we're writing. * Bit 1 is the BVEC_FLAG_NO_REF bit, set if type is a bvec and * the caller isn't expecting to drop a page reference when done. */ unsignedint type; size_t iov_offset; size_t count; union{ (···) structpipe_inode_info *pipe; }; (···) };
wget https://download.qemu.org/qemu-6.2.0.tar.xz mkdir build && cd build # 在下载目录新建文件夹build(这是必须的,因为configure命令必须在build文件夹下执行) # 以下均在/build目录下 ../configure make # 编译源码 make install # 安装
这得老半天了
Linux
选用 v5.13-rc1 版本
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wget https://github.com/torvalds/linux/archive/refs/tags/v5.13-rc1.tar.gz make menuconfig cat /proc/cpuinfo| grep "cpu cores" | uniq # check cpu core counts make bzImage -j4
扣y选中
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kernel hacking ->compile-time checks and compiler opt -> compile the kernel with debug info -> Provide GDB scripts for kernel debugging -> Generate readable assembler code kernel hacking -> compile the kernel with frame pointers (没找到) kernel hacking -> Generic Kernel Debugging Instruments -> KGDB: kernel debugger -> KGDB: use kgdb over the serial console (NEW)
If fd_in refers to a pipe, then off_in must be NULL
If fd_in does not refer to a pipe and off_in is NULL, then bytes are read from fd_in starting from the file offset, and the file offset is adjusted appropriately.
/** * Create a pipe where all "bufs" on the pipe_inode_info ring have the * PIPE_BUF_FLAG_CAN_MERGE flag set. */ staticvoidprepare_pipe(int p[2]) { if (pipe(p)) abort();
/* fill the pipe completely; each pipe_buffer will now have the PIPE_BUF_FLAG_CAN_MERGE flag */ for (unsigned r = pipe_size; r > 0;) { unsigned n = r > sizeof(buffer) ? sizeof(buffer) : r; write(p[1], buffer, n); r -= n; }
/* drain the pipe, freeing all pipe_buffer instances (but leaving the flags initialized) */ for (unsigned r = pipe_size; r > 0;) { unsigned n = r > sizeof(buffer) ? sizeof(buffer) : r; read(p[0], buffer, n); r -= n; }
/* the pipe is now empty, and if somebody adds a new pipe_buffer without initializing its "flags", the buffer will be mergeable */ }
/* open the input file and validate the specified offset */ constint fd = open(path, O_RDONLY); // yes, read-only! :-) if (fd < 0) { perror("open failed"); return EXIT_FAILURE; }
structstatst; if (fstat(fd, &st)) { perror("stat failed"); return EXIT_FAILURE; }
if (offset > st.st_size) { fprintf(stderr, "Offset is not inside the file\n"); return EXIT_FAILURE; }
if (end_offset > st.st_size) { fprintf(stderr, "Sorry, cannot enlarge the file\n"); return EXIT_FAILURE; }
/* create the pipe with all flags initialized with PIPE_BUF_FLAG_CAN_MERGE */ int p[2]; prepare_pipe(p);
/* splice one byte from before the specified offset into the pipe; this will add a reference to the page cache, but since copy_page_to_iter_pipe() does not initialize the "flags", PIPE_BUF_FLAG_CAN_MERGE is still set */ --offset; ssize_t nbytes = splice(fd, &offset, p[1], NULL, 1, 0); if (nbytes < 0) { perror("splice failed"); return EXIT_FAILURE; } if (nbytes == 0) { fprintf(stderr, "short splice\n"); return EXIT_FAILURE; }
/* the following write will not create a new pipe_buffer, but will instead write into the page cache, because of the PIPE_BUF_FLAG_CAN_MERGE flag */ nbytes = write(p[1], data, data_size); if (nbytes < 0) { perror("write failed"); return EXIT_FAILURE; } if ((size_t)nbytes < data_size) { fprintf(stderr, "short write\n"); return EXIT_FAILURE; }