stop using mmap for zip I/O

[Christos Zoulas]

Hi,

There are numerous bug reports about the jvm crashing in libzip...
Just google for "libzip java crash". The bottom line is that using
mmap is problematic (I can get into more per OS details if necessary)
because it will potentially signal when the file size is altered.
Can we please turn USE_MMAP off, and/or remove the code (zip_util.c)?
I don't think it is acceptable for the jvm to crash if it tries to
read a file while it is being modified. The following simple program
demonstrates the issue... just:

$ cc mmap.c
$ cp a.out b.out
$ ./a.out b.out

Best,

christos

$ cat << _EOF > mmap.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <err.h>
#include <signal.h>

#include <sys/mman.h>
#include <sys/stat.h>

volatile size_t i;
size_t size = 0;

void
sig(int s)
{
        printf("boom %d %zu\n", s, i);
        exit(1);
}

void
compute(unsigned char *v)
{
        int j = 0;
        for (i = 0; i < size; i++)
                j += v[i];
        printf("%d\n", j);
}

int
main(int argc, char *argv[])
{
        struct stat st;
        unsigned char *v;
        int fd;

        signal(SIGSEGV, sig);
        signal(SIGBUS, sig);
        fd = open(argv[1], O_RDONLY);
        if (fd == -1)
                err(1, "open %s", argv[1]);

        if (fstat(fd, &st) == -1)
                err(1, "fstat %s", argv[1]);
        size = st.st_size;
        if (size == 0)
                errx(1, "0 sized file");
        
        v = mmap(0, size, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0);
        if (v == MAP_FAILED)
                err(1, "mmap");

        printf("go1\n");
        compute(v);
        truncate(argv[1], 0);
        printf("go2\n");
        compute(v);
        return 0;
}
_EOF