[PATCH v2 1/7] iio: core: add read_avail_release_resource callback to fix race

[Matteo Martelli <matteomartelli3@gmail.com>]

Some iio drivers currently share an available info buffer that might be
changed while iio core prints it to sysfs. To avoid the buffer
corruption, add a release callback to let iio drivers allocate a copy of
the available info buffer and later free it in the release callback.
Such control is kept in the driver logic so that some driver that needs
a big available info buffer might also perform some check to keep the
copied buffer around in case no race has occurred.

Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
---
 drivers/iio/industrialio-core.c | 14 +++++++++++---
 include/linux/iio/iio.h         |  4 ++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 6a6568d4a2cb3a3f63381d5a6f25a2881b3ba2ed..4aea9de9f15a4d70f9d02fb3d47df49eef8c8423 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -859,12 +859,20 @@ static ssize_t iio_read_channel_info_avail(struct device *dev,
 		return ret;
 	switch (ret) {
 	case IIO_AVAIL_LIST:
-		return iio_format_avail_list(buf, vals, type, length);
+		ret = iio_format_avail_list(buf, vals, type, length);
+		break;
 	case IIO_AVAIL_RANGE:
-		return iio_format_avail_range(buf, vals, type);
+		ret = iio_format_avail_range(buf, vals, type);
+		break;
 	default:
-		return -EINVAL;
+		ret = -EINVAL;
 	}
+
+	if (indio_dev->info->read_avail_release_resource)
+		indio_dev->info->read_avail_release_resource(
+			indio_dev, this_attr->c, vals, this_attr->address);
+
+	return ret;
 }
 
 /**
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 18779b631e9071801958fc9d50b941b548fab940..55326f0310b2e9b3fa561c4728e7eabe1d7a5e78 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -491,6 +491,10 @@ struct iio_info {
 			  int *length,
 			  long mask);
 
+	void (*read_avail_release_resource)(struct iio_dev *indio_dev,
+					    struct iio_chan_spec const *chan,
+					    const int *vals, long mask);
+
 	int (*write_raw)(struct iio_dev *indio_dev,
 			 struct iio_chan_spec const *chan,
 			 int val,

-- 
2.46.2