[PATCH v2 4/5] ioctl_userfaultfd.2: fix / update UFFDIO_REGISTER error code list

[Axel Rasmussen <axelrasmussen@google.com>]

The list of error codes in the man page was out of date with respect to
the current state of the kernel. Some errors were partially /
incorrectly described.

Update the error code listing, so it matches the current state of the
kernel, and correctly describes all the errors.

Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
---
 man2/ioctl_userfaultfd.2 | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index 2ee6a0532..95d69f773 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -388,12 +388,6 @@ On error, \-1 is returned and
 .I errno
 is set to indicate the error.
 Possible errors include:
-.\" FIXME Is the following error list correct?
-.\"
-.TP
-.B EBUSY
-A mapping in the specified range is registered with another
-userfaultfd object.
 .TP
 .B EFAULT
 .I argp
@@ -408,21 +402,32 @@ field; or the
 field was zero.
 .TP
 .B EINVAL
-There is no mapping in the specified address range.
-.TP
-.B EINVAL
+The specified address range was invalid.
+More specifically,
+no mapping exists in the given range,
+or the mapping that exists there is invalid
+(e.g. unsupported type of memory),
+or the range values (
 .I range.start
 or
 .I range.len
-is not a multiple of the system page size; or,
+) are not multiples of the relevant page size,
+or
 .I range.len
-is zero; or these fields are otherwise invalid.
+is zero.
 .TP
-.B EINVAL
-There as an incompatible mapping in the specified address range.
-.\" Mike Rapoport:
-.\" ENOMEM if the process is exiting and the
-.\" mm_struct has gone by the time userfault grabs it.
+.B ENOMEM
+The process is exiting,
+and its address space has already been torn down
+when userfaultfd attempts to reference it.
+.TP
+.B EPERM
+The userfaultfd would allow writing to a file backing the mapping,
+but the calling process lacks such write permissions.
+.TP
+.B EBUSY
+A mapping in the specified range is registered with another
+userfaultfd object.
 .SS UFFDIO_UNREGISTER
 (Since Linux 4.3.)
 Unregister a memory address range from userfaultfd.
-- 
2.42.0.609.gbb76f46606-goog