[PATCH 2/5] pstore: Introduce write_buf backend callback

[Anton Vorontsov <anton.vorontsov@linaro.org>]

For function tracing we need to stop using pstore.buf directly, since
in a tracing callback we can't use spinlocks, and thus we can't safely
use the global buffer.

With write_buf callback, backends no longer need to access pstore.buf
directly, and thus we can pass any buffers (e.g. allocated on stack).

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 fs/pstore/platform.c   |   10 ++++++++++
 include/linux/pstore.h |    4 ++++
 2 files changed, 14 insertions(+)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index be4614f..e7c0a52 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -198,6 +198,14 @@ static void pstore_register_console(void)
 static void pstore_register_console(void) {}
 #endif
 
+static int pstore_write_compat(enum pstore_type_id type,
+			       enum kmsg_dump_reason reason,
+			       u64 *id, unsigned int part,
+			       size_t size, struct pstore_info *psi)
+{
+	return psi->write_buf(type, reason, id, part, psinfo->buf, size, psi);
+}
+
 /*
  * platform specific persistent storage driver registers with
  * us here. If pstore is already mounted, call the platform
@@ -222,6 +230,8 @@ int pstore_register(struct pstore_info *psi)
 		return -EINVAL;
 	}
 
+	if (!psi->write)
+		psi->write = pstore_write_compat;
 	psinfo = psi;
 	mutex_init(&psinfo->read_mutex);
 	spin_unlock(&pstore_lock);
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index 1bd014b..b107484 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -48,6 +48,10 @@ struct pstore_info {
 	int		(*write)(enum pstore_type_id type,
 			enum kmsg_dump_reason reason, u64 *id,
 			unsigned int part, size_t size, struct pstore_info *psi);
+	int		(*write_buf)(enum pstore_type_id type,
+			enum kmsg_dump_reason reason, u64 *id,
+			unsigned int part, const char *buf, size_t size,
+			struct pstore_info *psi);
 	int		(*erase)(enum pstore_type_id type, u64 id,
 			struct pstore_info *psi);
 	void		*data;
-- 
1.7.9.2