64 lines
1.7 KiB
C
64 lines
1.7 KiB
C
#include <sys/mman.h>
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#include <sys/stat.h>
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#include <err.h>
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#include <fcntl.h>
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#include <inttypes.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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int
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main(int argc, char **argv)
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{
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unsigned char byte;
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char *end;
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void *map;
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uintmax_t raw_offset;
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off_t map_offset, offset;
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size_t delta, pagesize;
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struct stat sb;
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int fd;
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if (argc != 3)
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errx(2, "usage: sparse_hole_probe file offset");
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raw_offset = strtoumax(argv[2], &end, 0);
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if (*argv[2] == '\0' || *end != '\0' || raw_offset > INT64_MAX)
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errx(2, "invalid offset: %s", argv[2]);
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offset = (off_t)raw_offset;
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pagesize = (size_t)getpagesize();
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map_offset = offset & ~((off_t)pagesize - 1);
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delta = (size_t)(offset - map_offset);
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fd = open(argv[1], O_RDONLY);
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if (fd < 0)
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err(1, "open %s", argv[1]);
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if (fstat(fd, &sb) != 0)
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err(1, "fstat %s", argv[1]);
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if (offset < 0 || offset >= sb.st_size ||
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sb.st_size - offset < (off_t)(pagesize - delta))
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errx(1, "probe page is outside the file");
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if (pread(fd, &byte, 1, offset) != 1)
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err(1, "pread at %jd", (intmax_t)offset);
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if (byte != 0)
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errx(1, "pread returned non-zero byte %#x", byte);
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map = mmap(NULL, pagesize, PROT_READ, MAP_PRIVATE, fd, map_offset);
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if (map == MAP_FAILED)
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err(1, "mmap at %jd", (intmax_t)map_offset);
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if (madvise(map, pagesize, MADV_DONTNEED) != 0)
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err(1, "madvise");
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if (((const unsigned char *)map)[delta] != 0 ||
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((const unsigned char *)map)[pagesize - 1] != 0)
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errx(1, "mmap returned non-zero hole data");
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if (munmap(map, pagesize) != 0)
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err(1, "munmap");
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if (close(fd) != 0)
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err(1, "close");
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printf("PASS size=%jd offset=%jd pread=zero mmap-page=zero\n",
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(intmax_t)sb.st_size, (intmax_t)offset);
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return (0);
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}
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