linux-kernel - Re: [PATCH v2 4/5] ioctl_userfaultfd.2: fix / update UFFDIO

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Message-ID: <ZSMn-H_BUmJMi9La@debian>
Date:   Mon, 9 Oct 2023 00:06:48 +0200
From:   Alejandro Colomar <alx@...nel.org>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Peter Xu <peterx@...hat.com>, linux-man@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v2 4/5] ioctl_userfaultfd.2: fix / update UFFDIO_REGISTER
 error code list

Hi Axel,

On Tue, Oct 03, 2023 at 12:45:46PM -0700, Axel Rasmussen wrote:
> The list of error codes in the man page was out of date with respect to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 | 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 (

This produces some unwanted space.  Please apply the following fix to
your patch.

diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index 6e954e98c..795014794 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -432,11 +432,11 @@ .SS UFFDIO_REGISTER
 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 the range values
+.IR ( range.start
 or
-.I range.len
-) are not multiples of the relevant page size,
+.IR range.len )
+are not multiples of the relevant page size,
 or
 .I range.len
 is zero.

>  .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.

Why would you move EBUSY to the end?  Do you see any reasons to order it
that way?

Thanks,
Alex

>  .SS UFFDIO_UNREGISTER
>  (Since Linux 4.3.)
>  Unregister a memory address range from userfaultfd.
> -- 
> 2.42.0.609.gbb76f46606-goog
> 

-- 
<https://www.alejandro-colomar.es/>

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