Re: [PATCH v2 3/5] selftests/mm: move write_file helper to vm_util

Mike Rapoport
2026-03-16T06:35:25Z

On Mon, Mar 16, 2026 at 12:43:33PM +0800, Chunyu Hu wrote:
> thp_settings provides write_file() helper for safely writing to a file and
> exit when write failure happens. It's a very low level helper and many sub
> tests need such a helper, not only thp tests.
>
> split_huge_page_test also defines a write_file locally. The two have minior
> differences in return type and used exit api. And there would be conflicts
> if split_huge_page_test wanted to include thp_settings.h because of
> different prototype, making it less convenient.
>
> It's possisble to merge the two, although some tests don't use the
> kselftest infrastrucutre for testing. It would also work when using the
> ksft_exit_msg() to exit in my test, as the counters are all zero. Output
> will be like:
>
> TAP version 13
> 1..62
> Bail out! /proc/sys/vm/drop_caches1 open failed: No such file or directory
> # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0
>
> So here just leave one version of write_file, and move it into the vm_util.
> This make it easy to maitain and user could just include one vm_util.h when
> then don't need thp setting helpers. Keep the prototype of returning the
> written bytes num.
>
> Suggested-by: Mike Rapoport <rppt@kernel.org>
> Signed-off-by: Chunyu Hu <chuhu@redhat.com>
> ---
> Changes in v2:
> new patch from v2
> ---
> .../selftests/mm/split_huge_page_test.c | 15 ------------
> tools/testing/selftests/mm/thp_settings.c | 24 +------------------
> tools/testing/selftests/mm/thp_settings.h | 1 -
> tools/testing/selftests/mm/vm_util.c | 16 +++++++++++++
> tools/testing/selftests/mm/vm_util.h | 2 ++
> 5 files changed, 19 insertions(+), 39 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
> index e0167111bdd1..93f205327b84 100644
> --- a/tools/testing/selftests/mm/split_huge_page_test.c
> +++ b/tools/testing/selftests/mm/split_huge_page_test.c
> @@ -255,21 +255,6 @@ static int check_after_split_folio_orders(char *vaddr_start, size_t len,
> return status;
> }
>
> -static void write_file(const char *path, const char *buf, size_t buflen)
> -{
> - int fd;
> - ssize_t numwritten;
> -
> - fd = open(path, O_WRONLY);
> - if (fd == -1)
> - ksft_exit_fail_msg("%s open failed: %s\n", path, strerror(errno));
> -
> - numwritten = write(fd, buf, buflen - 1);
> - close(fd);
> - if (numwritten < 1)
> - ksft_exit_fail_msg("Write failed\n");
> -}
> -
> static void write_debugfs(const char *fmt, ...)
> {
> char input[INPUT_MAX];
> diff --git a/tools/testing/selftests/mm/thp_settings.c b/tools/testing/selftests/mm/thp_settings.c
> index 574bd0f8ae48..02de28ecf31a 100644
> --- a/tools/testing/selftests/mm/thp_settings.c
> +++ b/tools/testing/selftests/mm/thp_settings.c
> @@ -6,6 +6,7 @@
> #include <string.h>
> #include <unistd.h>
>
> +#include "vm_util.h"
> #include "thp_settings.h"
>
> #define THP_SYSFS "/sys/kernel/mm/transparent_hugepage/"
> @@ -64,29 +65,6 @@ int read_file(const char *path, char *buf, size_t buflen)
> return (unsigned int) numread;
> }
>
> -int write_file(const char *path, const char *buf, size_t buflen)
> -{
> - int fd;
> - ssize_t numwritten;
> -
> - fd = open(path, O_WRONLY);
> - if (fd == -1) {
> - printf("open(%s)\n", path);
> - exit(EXIT_FAILURE);
> - return 0;
> - }
> -
> - numwritten = write(fd, buf, buflen - 1);
> - close(fd);
> - if (numwritten < 1) {
> - printf("write(%s)\n", buf);
> - exit(EXIT_FAILURE);
> - return 0;
> - }
> -
> - return (unsigned int) numwritten;
> -}
> -
> unsigned long read_num(const char *path)
> {
> char buf[21];
> diff --git a/tools/testing/selftests/mm/thp_settings.h b/tools/testing/selftests/mm/thp_settings.h
> index 76eeb712e5f1..7748a9009191 100644
> --- a/tools/testing/selftests/mm/thp_settings.h
> +++ b/tools/testing/selftests/mm/thp_settings.h
> @@ -63,7 +63,6 @@ struct thp_settings {
> };
>
> int read_file(const char *path, char *buf, size_t buflen);
> -int write_file(const char *path, const char *buf, size_t buflen);
> unsigned long read_num(const char *path);
> void write_num(const char *path, unsigned long num);
>
> diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
> index a6d4ff7dfdc0..b4b3b48f8dc9 100644
> --- a/tools/testing/selftests/mm/vm_util.c
> +++ b/tools/testing/selftests/mm/vm_util.c
> @@ -764,3 +764,19 @@ int unpoison_memory(unsigned long pfn)
>
> return ret > 0 ? 0 : -errno;
> }
> +
> +unsigned int write_file(const char *path, const char *buf, size_t buflen)
> +{
> + int fd;
> + ssize_t numwritten;
> +
> + fd = open(path, O_WRONLY);
> + if (fd == -1)
> + ksft_exit_fail_msg("%s open failed: %s\n", path, strerror(errno));
> +
> + numwritten = write(fd, buf, buflen - 1);
> + close(fd);
> + if (numwritten < 1)
> + ksft_exit_fail_msg("Write failed\n");
> + return (unsigned int) numwritten;

If we exit on any failure, the function can be void just like in
split_huge_page_test.c. This will also simplify write_num() and read_num()
in thp_settigns.c

> +}
> diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> index e9c4e24769c1..22c8805e0d7a 100644
> --- a/tools/testing/selftests/mm/vm_util.h
> +++ b/tools/testing/selftests/mm/vm_util.h
> @@ -166,3 +166,5 @@ int unpoison_memory(unsigned long pfn);
>
> #define PAGEMAP_PRESENT(ent) (((ent) & (1ull << 63)) != 0)
> #define PAGEMAP_PFN(ent) ((ent) & ((1ull << 55) - 1))
> +
> +unsigned int write_file(const char *path, const char *buf, size_t buflen);
> --
> 2.53.0
>

--
Sincerely yours,
Mike.