[Qemu-devel] [PATCH 11/23] userfaultfd: Rename uffd_api.bits into .features

[Andrea Arcangeli]

From: Pavel Emelyanov <address@hidden>

This is (seem to be) the minimal thing that is required to unblock
standard uffd usage from the non-cooperative one. Now more bits can
be added to the features field indicating e.g. UFFD_FEATURE_FORK and
others needed for the latter use-case.

Signed-off-by: Pavel Emelyanov <address@hidden>
Signed-off-by: Andrea Arcangeli <address@hidden>
---
 fs/userfaultfd.c                 |  4 ++--
 include/uapi/linux/userfaultfd.h | 10 ++++++++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 1c9be61..9085365 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -856,7 +856,7 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
                goto out;
        }
        /* careful not to leak info, we only read the first 8 bytes */
-       uffdio_api.bits = UFFD_API_BITS;
+       uffdio_api.features = UFFD_API_FEATURES;
        uffdio_api.ioctls = UFFD_API_IOCTLS;
        ret = -EFAULT;
        if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
@@ -913,7 +913,7 @@ static void userfaultfd_show_fdinfo(struct seq_file *m, 
struct file *f)
         *      protocols: aa:... bb:...
         */
        seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
-                  pending, total, UFFD_API, UFFD_API_BITS,
+                  pending, total, UFFD_API, UFFD_API_FEATURES,
                   UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
 }
 #endif
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 9a8cd56..5e1c2f7 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -11,7 +11,7 @@
 
 #define UFFD_API ((__u64)0xAA)
 /* FIXME: add "|UFFD_BIT_WP" to UFFD_API_BITS after implementing it */
-#define UFFD_API_BITS (UFFD_BIT_WRITE)
+#define UFFD_API_FEATURES (UFFD_FEATURE_WRITE_BIT)
 #define UFFD_API_IOCTLS                                \
        ((__u64)1 << _UFFDIO_REGISTER |         \
         (__u64)1 << _UFFDIO_UNREGISTER |       \
@@ -51,12 +51,18 @@
 #define UFFD_BIT_WP    (1<<1)  /* handle_userfault() reason VM_UFFD_WP */
 #define UFFD_BITS      2       /* two above bits used for UFFD_BIT_* mask */
 
+/*
+ * Features reported in uffdio_api.features field
+ */
+#define UFFD_FEATURE_WRITE_BIT (1<<0) /* Corresponds to UFFD_BIT_WRITE */
+#define UFFD_FEATURE_WP_BIT    (1<<1) /* Corresponds to UFFD_BIT_WP */
+
 struct uffdio_api {
        /* userland asks for an API number */
        __u64 api;
 
        /* kernel answers below with the available features for the API */
-       __u64 bits;
+       __u64 features;
        __u64 ioctls;
 };