core: relax gpiod_is_gpiochip_device() even more

Currently libgpiod requires that the GPIO chip character device be named
'gpiochip%u' in devfs. However it's a perfectly valid use-case to have
the device file renamed by udev (or equivalent) to anything else.

Modify gpiod_is_gpiochip_device() to check the major and minor device
numbers first and then ensure that the device in question is associated
with the GPIO subsystem. No longer check the name.

Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

diff --git a/lib/core.c b/lib/core.c
index c1fb8ec2e010d3fb667853a46e737edc0925b9e8..32c4238a500b27c86520f712bfc38cc5a41b20e2 100644 (file)
--- a/lib/core.c
+++ b/lib/core.c
@@ -182,11 +182,10 @@ GPIOD_API void gpiod_line_bulk_foreach_line(struct gpiod_line_bulk *bulk,
 
 GPIOD_API bool gpiod_is_gpiochip_device(const char *path)
 {
-       char *name, *realname, *sysfsp, sysfsdev[16], devstr[16];
+       char *realname, *sysfsp, devpath[64];
        struct stat statbuf;
        bool ret = false;
-       int rv, fd;
-       ssize_t rd;
+       int rv;
 
        rv = lstat(path, &statbuf);
        if (rv)
@@ -217,15 +216,15 @@ GPIOD_API bool gpiod_is_gpiochip_device(const char *path)
                goto out_free_realname;
        }
 
-       /* Get the basename. */
-       name = basename(realname);
+       /* Is the device associated with the GPIO subsystem? */
+       snprintf(devpath, sizeof(devpath), "/sys/dev/char/%u:%u/subsystem",
+                major(statbuf.st_rdev), minor(statbuf.st_rdev));
 
-       /* Do we have a corresponding sysfs attribute? */
-       rv = asprintf(&sysfsp, "/sys/bus/gpio/devices/%s/dev", name);
-       if (rv < 0)
+       sysfsp = realpath(devpath, NULL);
+       if (!sysfsp)
                goto out_free_realname;
 
-       if (access(sysfsp, R_OK) != 0) {
+       if (strcmp(sysfsp, "/sys/bus/gpio") != 0) {
                /*
                 * This is a character device but not the one we're after.
                 * Before the introduction of this function, we'd fail with
@@ -237,30 +236,6 @@ GPIOD_API bool gpiod_is_gpiochip_device(const char *path)
                goto out_free_sysfsp;
        }
 
-       /*
-        * Make sure the major and minor numbers of the character device
-        * correspond to the ones in the dev attribute in sysfs.
-        */
-       snprintf(devstr, sizeof(devstr), "%u:%u",
-                major(statbuf.st_rdev), minor(statbuf.st_rdev));
-
-       fd = open(sysfsp, O_RDONLY);
-       if (fd < 0)
-               goto out_free_sysfsp;
-
-       memset(sysfsdev, 0, sizeof(sysfsdev));
-       rd = read(fd, sysfsdev, sizeof(sysfsdev) - 1);
-       close(fd);
-       if (rd < 0)
-               goto out_free_sysfsp;
-
-       rd--; /* Ignore trailing newline. */
-       if ((size_t)rd != strlen(devstr) ||
-           strncmp(sysfsdev, devstr, rd) != 0) {
-               errno = ENODEV;
-               goto out_free_sysfsp;
-       }
-
        ret = true;
 
 out_free_sysfsp: