2 files changed, 17 insertions, 0 deletions

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 30faf797c2c3..d4e01b358341 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -179,6 +179,7 @@ struct kernfs_open_file {
         struct mutex            mutex;
         int                     event;
         struct list_head        list;
+        char                    *prealloc_buf;
 
         size_t                  atomic_write_len;
         bool                    mmapped;
@@ -214,6 +215,13 @@ struct kernfs_ops {
          * larger ones are rejected with -E2BIG.
          */
         size_t atomic_write_len;
+        /*
+         * "prealloc" causes a buffer to be allocated at open for
+         * all read/write requests.  As ->seq_show uses seq_read()
+         * which does its own allocation, it is incompatible with
+         * ->prealloc.  Provide ->read and ->write with ->prealloc.
+         */
+        bool prealloc;
         ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
                          loff_t off);
 
diff --git a/include/linux/sysfs.h b/include/linux/sysfs.h
index f97d0dbb59fa..ddad16148bd6 100644
--- a/include/linux/sysfs.h
+++ b/include/linux/sysfs.h
@@ -70,6 +70,8 @@ struct attribute_group {
  * for examples..
  */
 
+#define SYSFS_PREALLOC 010000
+
 #define __ATTR(_name, _mode, _show, _store) {                           \
         .attr = {.name = __stringify(_name),                            \
                  .mode = VERIFY_OCTAL_PERMISSIONS(_mode) },             \
@@ -77,6 +79,13 @@ struct attribute_group {
         .store  = _store,                                               \
 }
 
+#define __ATTR_PREALLOC(_name, _mode, _show, _store) {                  \
+        .attr = {.name = __stringify(_name),                            \
+                 .mode = SYSFS_PREALLOC | VERIFY_OCTAL_PERMISSIONS(_mode) },\
+        .show   = _show,                                                \
+        .store  = _store,                                               \
+}
+
 #define __ATTR_RO(_name) {                                              \
         .attr   = { .name = __stringify(_name), .mode = S_IRUGO },      \
         .show   = _name##_show,                                         \