engines/devdax: Make detection of device-dax instances more robust

In preparation for the kernel switching device-dax instances from the
"/sys/class/dax" subsystem to "/sys/bus/dax" [1], teach the device-dax
instance detection to be subsystem-type agnostic.

Note that the subsystem switch will require an administrator, or distro
opt-in. The opt-in will either be at kernel compile time by disabling
the default compatibility driver in the kernel, or at runtime with a
modprobe policy to override which kernel module service device-dax
devices. The daxctl utility [2] will ship a command to install the
modprobe policy and include a man page that lists the potential
regression risk to older FIO and other userspace tools that are hard
coded to "/sys/class/dax".

[1]: https://lwn.net/Articles/770128/
[2]: https://github.com/pmem/ndctl/tree/master/daxctl

Reported-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/engines/dev-dax.c b/engines/dev-dax.c
index 0660bba563e6a4a522ba5ace408b78ffe4744e3c..422ea634ff1d2530b6dae4ba40747417281ee27c 100644 (file)
--- a/engines/dev-dax.c
+++ b/engines/dev-dax.c
@@ -259,7 +259,7 @@ fio_devdax_get_file_size(struct thread_data *td, struct fio_file *f)
 {
        char spath[PATH_MAX];
        char npath[PATH_MAX];
-       char *rpath;
+       char *rpath, *basename;
        FILE *sfile;
        uint64_t size;
        struct stat st;
@@ -289,7 +289,8 @@ fio_devdax_get_file_size(struct thread_data *td, struct fio_file *f)
        }
 
        /* check if DAX device */
-       if (strcmp("/sys/class/dax", rpath)) {
+       basename = strrchr(rpath, '/');
+       if (!basename || strcmp("dax", basename+1)) {
                log_err("%s: %s not a DAX device!\n",
                        td->o.name, f->file_name);
        }