Hi,
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 <xemul@xxxxxxxxxxxxx>
---
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index d2db3e1..c4d0216 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1090,7 +1090,7 @@ 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)))
@@ -1159,7 +1159,7 @@ 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 aecd64b..3dc0cba 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 | \
@@ -63,12 +63,18 @@
#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;
};
--
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