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SubjectRe: [PATCH] mm/selftest: Add MAP_POPULATE test
On Thu,  2 Aug 2018 00:36:36 +0100 Dmitry Safonov <dima@arista.com> wrote:

> As many other projects, we use some shmalloc allocator.
> At some point we need to make a part of allocated pages back private to
> process. And it should be populated straight away.
> Check that (MAP_PRIVATE | MAP_POPULATE) actually copies the private page.
>
> ...
>
> --- /dev/null
> +++ b/tools/testing/selftests/vm/map_populate.c
>
> ...
>
> +#define BUG_ON(condition, description) \
> + do { \
> + if (condition) { \
> + fprintf(stderr, "[FAIL]\t%s:%d\t%s:%s\n", __func__, \
> + __LINE__, (description), strerror(errno)); \
> + exit(1); \
> + } \
> + } while (0)

This is userspace. Why not use assert()?

>
> ...
>
> +int main(int argc, char **argv)
> +{
> + int sock[2], child, ret;
> + FILE *ftmp;
> + unsigned long *smap;
> +
> + ftmp = tmpfile();

Seems odd to putz around with stdio when you just want the fd.
mkstemp(), maybe?

> + BUG_ON(ftmp == 0, "tmpfile()");
> +
> + ret = ftruncate(fileno(ftmp), MMAP_SZ);
> + BUG_ON(ret, "ftruncate()");
> +
> + smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,
> + MAP_SHARED, fileno(ftmp), 0);
> + BUG_ON(smap == MAP_FAILED, "mmap()");
> +
> + *smap = 0xdeadbabe;
> + /* Probably unnecessary, but let it be. */
> + ret = msync(smap, MMAP_SZ, MS_SYNC);
> + BUG_ON(ret, "msync()");
> +
> + ret = socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sock);
> + BUG_ON(ret, "socketpair()");
> +
> + child = fork();
> + BUG_ON(child == -1, "fork()");
> +
> + if (child) {
> + ret = close(sock[0]);
> + BUG_ON(ret, "close()");
> +
> + return parent_f(sock[1], smap, child);
> + }
> +
> + ret = close(sock[1]);
> + BUG_ON(ret, "close()");
> +
> + return child_f(sock[0], smap, fileno(ftmp));
> +}
>
> ...
>

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