selftests/mm: skip map_populate on weird filesystems

It seems that 9pfs does not allow truncating unlinked files, Mark Brown
has noted that NFS may also behave this way.

It doesn't seem quite right to call this a "bug" but it's probably a
special enough case that it makes sense for the test to just SKIP if it
happens.

Link: https://lkml.kernel.org/r/20250221-mm-selftests-v2-8-28c4d66383c5@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/tools/testing/selftests/mm/map_populate.c b/tools/testing/selftests/mm/map_populate.c
index 5c8a53869b1bd287b09a250edf628a66c25c2439..cdd88531dd9fe98f2d25edf4878659767c919e8e 100644 (file)
--- a/tools/testing/selftests/mm/map_populate.c
+++ b/tools/testing/selftests/mm/map_populate.c
@@ -87,6 +87,13 @@ int main(int argc, char **argv)
        BUG_ON(!ftmp, "tmpfile()");
 
        ret = ftruncate(fileno(ftmp), MMAP_SZ);
+       if (ret < 0 && errno == ENOENT) {
+               /*
+                * This probably means tmpfile() made a file on a filesystem
+                * that doesn't handle temporary files the way we want.
+                */
+               ksft_exit_skip("ftruncate(fileno(tmpfile())) gave ENOENT, weird filesystem?");
+       }
        BUG_ON(ret, "ftruncate()");
 
        smap = mmap(0, MMAP_SZ, PROT_READ | PROT_WRITE,