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

[Chunyu Hu <chuhu@redhat.com>]

On Mon, Mar 16, 2026 at 08:35:11AM +0200, Mike Rapoport wrote:
> 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

Good point. I will change it to void. I wont touch read_file() here.

> 
> > +}
> > 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.
>