linux-kernel - [PATCH v3 2/3] ioctl_userfaultfd.2: fix / update UFFDIO

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Date:   Tue, 17 Oct 2023 16:01:09 -0700
From:   Axel Rasmussen <axelrasmussen@...gle.com>
To:     Alejandro Colomar <alx@...nel.org>,
        Mike Rapoport <rppt@...nel.org>, Peter Xu <peterx@...hat.com>
Cc:     linux-man@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Axel Rasmussen <axelrasmussen@...gle.com>
Subject: [PATCH v3 2/3] ioctl_userfaultfd.2: fix / update UFFDIO_REGISTER
 error code list

The list of error codes in the man page was out of date with respect to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@...gle.com>
---
 man2/ioctl_userfaultfd.2 | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index 82aee667c..40528001e 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -413,8 +413,6 @@ 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
@@ -433,21 +431,28 @@ field; or the
 field was zero.
 .TP
 .B EINVAL
-There is no mapping in the specified address range.
-.TP
-.B EINVAL
-.I range.start
+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
+.RI ( range.start
+or
+.IR range.len )
+are not multiples of the relevant page size,
 or
 .I range.len
-is not a multiple of the system 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.
 .SS UFFDIO_UNREGISTER
 (Since Linux 4.3.)
 Unregister a memory address range from userfaultfd.
-- 
2.42.0.655.g421f12c284-goog