channel: Support attribute names that start with the channel's label

Support attribute names that start with the channel's label to avoid
breaking compatibility with old kernels, which did not offer a 'label'
attribute, and caused Libiio to sometimes misdetect the channel's
extended name as being part of the attribute name.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

channel.c

@@ -344,21 +344,53 @@ const char * iio_channel_get_attr(const struct iio_channel *chn,
  return chn->attrs[index].name;
 }
 
-const char * iio_channel_find_attr(const struct iio_channel *chn,
- const char *name)
+static const char *
+iio_channel_do_find_attr(const struct iio_channel *chn, const char *name)
 {
  unsigned int i;
+
  for (i = 0; i < chn->nb_attrs; i++) {
  const char *attr = chn->attrs[i].name;
  if (!strcmp(attr, name))
  return attr;
  }
+
+ return NULL;
+}
+
+const char * iio_channel_find_attr(const struct iio_channel *chn,
+ const char *name)
+{
+ const char *attr;
+ size_t len;
+
+ attr = iio_channel_do_find_attr(chn, name);
+ if (attr)
+ return attr;
+
+ /* Support attribute names that start with the channel's label to avoid
+ * breaking compatibility with old kernels, which did not offer a
+ * 'label' attribute, and caused Libiio to sometimes misdetect the
+ * channel's extended name as being part of the attribute name. */
+ if (chn->name) {
+ len = strlen(chn->name);
+
+ if (!strncmp(chn->name, name, len) && name[len] == '_') {
+ name += len + 1;
+ return iio_channel_do_find_attr(chn, name);
+ }
+ }
+
  return NULL;
 }
 
 ssize_t iio_channel_attr_read(const struct iio_channel *chn,
  const char *attr, char *dst, size_t len)
 {
+ attr = iio_channel_find_attr(chn, attr);
+ if (!attr)
+ return -ENOENT;
+
  if (chn->dev->ctx->ops->read_channel_attr)
  return chn->dev->ctx->ops->read_channel_attr(chn,
  attr, dst, len);
@@ -369,6 +401,10 @@ ssize_t iio_channel_attr_read(const struct iio_channel *chn,
 ssize_t iio_channel_attr_write_raw(const struct iio_channel *chn,
  const char *attr, const void *src, size_t len)
 {
+ attr = iio_channel_find_attr(chn, attr);
+ if (!attr)
+ return -ENOENT;
+
  if (chn->dev->ctx->ops->write_channel_attr)
  return chn->dev->ctx->ops->write_channel_attr(chn,
  attr, src, len);