Re: [PATCH v5 3/6] selftests/mm: move write_file helper to vm_util

[Chunyu Hu <chuhu@redhat.com>]

On Mon, Mar 23, 2026 at 03:48:58PM +0000, Lorenzo Stoakes (Oracle) wrote:
> On Mon, Mar 23, 2026 at 11:17:50PM +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 we just keep the version in split_huge_page_test, and move it into
> > the vm_util. This makes it easy to maitain and user could just include one
> > vm_util.h when they don't need thp setting helpers. Keep the prototype of
> > void return as the function will exit on any error, return value is not
> > necessary, and will simply the callers like write_num() and write_string().
> >
> > Acked-by: David Hildenbrand (Arm) <david@kernel.org>
> > Reviewed-by: Zi Yan <ziy@nvidia.com>
> > Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> > Suggested-by: Mike Rapoport <rppt@kernel.org>
> > Signed-off-by: Chunyu Hu <chuhu@redhat.com>
> 
> I already reviewed this :) but easy to accidentally forget to propagate
> tags. Anyway, as before:
> 
> Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Sorry I forgot adding your review in my last version. I'll add in v6. Thanks
for your review!

> 
> Cheers, Lorenzo
> 
> > ---
> > Changes in v5:
> >   - updated acked-by and reviewed-by
> > Changes in v3:
> >   - make the write_file void return
> > Changes in v2:
> >   new patch from v2
> > ---
> >  .../selftests/mm/split_huge_page_test.c       | 15 --------
> >  tools/testing/selftests/mm/thp_settings.c     | 35 ++-----------------
> >  tools/testing/selftests/mm/thp_settings.h     |  1 -
> >  tools/testing/selftests/mm/vm_util.c          | 15 ++++++++
> >  tools/testing/selftests/mm/vm_util.h          |  2 ++
> >  5 files changed, 20 insertions(+), 48 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..e748ebfb3d4e 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];
> > @@ -104,10 +82,7 @@ void write_num(const char *path, unsigned long num)
> >  	char buf[21];
> >
> >  	sprintf(buf, "%ld", num);
> > -	if (!write_file(path, buf, strlen(buf) + 1)) {
> > -		perror(path);
> > -		exit(EXIT_FAILURE);
> > -	}
> > +	write_file(path, buf, strlen(buf) + 1);
> >  }
> >
> >  int thp_read_string(const char *name, const char * const strings[])
> > @@ -165,11 +140,7 @@ void thp_write_string(const char *name, const char *val)
> >  		printf("%s: Pathname is too long\n", __func__);
> >  		exit(EXIT_FAILURE);
> >  	}
> > -
> > -	if (!write_file(path, val, strlen(val) + 1)) {
> > -		perror(path);
> > -		exit(EXIT_FAILURE);
> > -	}
> > +	write_file(path, val, strlen(val) + 1);
> >  }
> >
> >  unsigned long thp_read_num(const char *name)
> > 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..ad96d19d1b85 100644
> > --- a/tools/testing/selftests/mm/vm_util.c
> > +++ b/tools/testing/selftests/mm/vm_util.c
> > @@ -764,3 +764,18 @@ int unpoison_memory(unsigned long pfn)
> >
> >  	return ret > 0 ? 0 : -errno;
> >  }
> > +
> > +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");
> > +}
> > diff --git a/tools/testing/selftests/mm/vm_util.h b/tools/testing/selftests/mm/vm_util.h
> > index e9c4e24769c1..1a07305ceff4 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))
> > +
> > +void write_file(const char *path, const char *buf, size_t buflen);
> > --
> > 2.53.0
> >
>