85 lines
1.7 KiB
C
85 lines
1.7 KiB
C
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#define _GNU_SOURCE
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#define _LARGEFILE64_SOURCE
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#include <assert.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <sys/mount.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include "buse.h"
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static int fd;
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static void usage(void)
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{
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fprintf(stderr, "Usage: loopback <phyical device> <virtual device>\n");
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}
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static int loopback_read(void *buf, u_int32_t len, u_int64_t offset)
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{
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int bytes_read;
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lseek64(fd, offset, SEEK_SET);
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while (len > 0) {
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bytes_read = read(fd, buf, len);
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assert(bytes_read > 0);
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len -= bytes_read;
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buf = (char *) buf + bytes_read;
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}
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return 0;
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}
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static int loopback_write(const void *buf, u_int32_t len, u_int64_t offset)
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{
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int bytes_written;
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lseek64(fd, offset, SEEK_SET);
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while (len > 0) {
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bytes_written = write(fd, buf, len);
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assert(bytes_written > 0);
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len -= bytes_written;
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buf = (char *) buf + bytes_written;
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}
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return 0;
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}
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static struct buse_operations bop = {
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.read = loopback_read,
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.write = loopback_write
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};
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int main(int argc, char *argv[])
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{
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struct stat buf;
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int err;
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int64_t size;
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if (argc != 3) {
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usage();
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return -1;
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}
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fd = open(argv[1], O_RDWR|O_LARGEFILE);
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assert(fd != -1);
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/* Let's verify that this file is actually a block device. We could support
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* regular files, too, but we don't need to right now. */
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fstat(fd, &buf);
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assert(S_ISBLK(buf.st_mode));
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/* Figure out the size of the underlying block device. */
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err = ioctl(fd, BLKGETSIZE64, &size);
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assert(err != -1);
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fprintf(stderr, "The size of this device is %ld bytes.\n", size);
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bop.size = size;
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buse_main(argc, argv, &bop, NULL);
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return 0;
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}
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