[PATCH v4] Implement decoding of ustat syscall

[Dmitry V. Levin]

On Mon, Jan 09, 2017 at 09:40:19PM +0800, JingPiao Chen wrote:
[...]
> +#include "tests.h"
> +#include <asm/unistd.h>
> +
> +#ifdef __NR_ustat
> +
> +# include <stdio.h>
> +# include <sys/stat.h>
> +# include <sys/sysmacros.h>
> +# include <unistd.h>
> +# include <ustat.h>
> +
> +int
> +main(void)
> +{
> +	kernel_ulong_t magic = (kernel_ulong_t) 0xfacefeedffffffff;
> +	unsigned int dev = (unsigned int) magic;
> +	struct ustat *ust = tail_alloc(sizeof(*ust));
> +	struct stat st;
> +
> +	long rc = syscall(__NR_ustat, magic, 0);
> +	printf("ustat(makedev(%u, %u), NULL) = %s\n", major(dev),
> +	       minor(dev), sprintrc(rc));

It'd look nicer if you wrapped the line after the first argument, e.g.

	printf("ustat(makedev(%u, %u), NULL) = %s\n",
	       major(dev), minor(dev), sprintrc(rc));

> +
> +	rc = syscall(__NR_ustat, magic, ust);
> +	printf("ustat(makedev(%u, %u), %p) = %s\n", major(dev), minor(dev),
> +	       ust, sprintrc(rc));

Likewise.

> +
> +	if (stat("/", &st) == -1)
> +		perror_msg_and_fail("stat");
> +	rc = syscall(__NR_ustat, st.st_dev, ust);

Please note that sizeof(st.st_dev) might be greater than sizeof(dev).
If this is the case, the value of st.st_dev might not be a valid argument
for ustat.  I suggest assigning st.st_dev to dev with a check that both
are equal.  If it is the case, you can pass dev on to ustat.

> +	printf("ustat(makedev(%u, %u), {f_tfree=%llu, f_tinode=%llu}) = %s\n",
> +	       major(st.st_dev), minor(st.st_dev), (unsigned long long) ust->f_tfree,
> +	       (unsigned long long) ust->f_tinode, sprintrc(rc));

Please note that ustat might be not implemented by the kernel,
so one cannot assume that a ustat call succeeds.


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