On Tue, Mar 24, 2026 at 09:33:14AM +0800, Chunyu Hu wrote:
> Add two more checks for buflen and numwritten. The buflen should be at
> least one, otherwise the 'buflen - 1' could underflow and cause trouble.
> The numwritten should be equal to 'buflen - 1'. The test will exit if
> any of these conditions aren't met.
>
> Additionally, add more print information when a write failure occurs or
> a truncated write happens, providing clearer diagnostics.
>
> Signed-off-by: Chunyu Hu <[email protected]>
> ---
> Changes in v6:
> - save/restore errno before and after the close(), so the log could show
> the correct error info on failure. Suggested by AI.
> Chagnes in v5:
> - new patch for making improve on write_file. Add more safety checks and
> diagnostics info in log
> ---
> tools/testing/selftests/mm/vm_util.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/vm_util.c
> b/tools/testing/selftests/mm/vm_util.c
> index ad96d19d1b85..572ccb99de8e 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -767,15 +767,23 @@ int unpoison_memory(unsigned long pfn)
>
> void write_file(const char *path, const char *buf, size_t buflen)
> {
> - int fd;
> + int fd, saved_errno;
> ssize_t numwritten;
> + if (buflen < 1)
> + ksft_exit_fail_msg("Incorrect buffer len: %zu\n", buflen);
>
> fd = open(path, O_WRONLY);
> if (fd == -1)
> ksft_exit_fail_msg("%s open failed: %s\n", path,
> strerror(errno));
We have ksft_exit_fail_perror(), fits great here
>
> numwritten = write(fd, buf, buflen - 1);
> + saved_errno = errno;
> close(fd);
> + errno = saved_errno;
> if (numwritten < 1)
> - ksft_exit_fail_msg("Write failed\n");
> + ksft_exit_fail_msg("%s write(%s) failed: %s\n", path, buf,
> + strerror(errno));
and here.
> + if (numwritten != buflen - 1)
> + ksft_exit_fail_msg("%s write(%s) is truncated, expected %zu
> bytes, got %zd bytes\n",
> + path, buf, buflen - 1, numwritten);
> }
> --
> 2.53.0
>
--
Sincerely yours,
Mike.
