| Message ID | 20231017230110.3170850-2-axelrasmussen@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | userfaultfd man page updates | expand |
On Tue, Oct 17, 2023 at 04:01:08PM -0700, Axel Rasmussen wrote: > The old FIXME noted that the zeroing was done to differentiate the two > EINVAL cases. It's possible something like this was true historically, > but in current Linux we zero it in *both* EINVAL cases, so this is at > least no longer true. > > After reading the code, I can't determine any clear reason why we zero > it in some cases but not in others. So, some simple advice we can give > userspace is: if an error occurs, treat the contents of the structure as > unspecified. Just re-initialize it before retrying UFFDIO_API again. > > Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org> > Signed-off-by: Axel Rasmussen <axelrasmussen@google.com> Hi Axel, Patch applied. Thanks, and thank you too Mike for the review. Cheers, Alex > --- > man2/ioctl_userfaultfd.2 | 16 ++++++++-------- > 1 file changed, 8 insertions(+), 8 deletions(-) > > diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 > index e68085262..82aee667c 100644 > --- a/man2/ioctl_userfaultfd.2 > +++ b/man2/ioctl_userfaultfd.2 > @@ -272,6 +272,14 @@ operation returns 0 on success. > On error, \-1 is returned and > .I errno > is set to indicate the error. > +If an error occurs, > +the kernel may zero the provided > +.I uffdio_api > +structure. > +The caller should treat its contents as unspecified, > +and reinitialize it before re-attempting another > +.B UFFDIO_API > +call. > Possible errors include: > .TP > .B EFAULT > @@ -305,14 +313,6 @@ feature was enabled, > but the calling process doesn't have the > .B CAP_SYS_PTRACE > capability. > -.\" FIXME In the above error case, the returned 'uffdio_api' structure is > -.\" zeroed out. Why is this done? This should be explained in the manual page. > -.\" > -.\" Mike Rapoport: > -.\" In my understanding the uffdio_api > -.\" structure is zeroed to allow the caller > -.\" to distinguish the reasons for -EINVAL. > -.\" > .SS UFFDIO_REGISTER > (Since Linux 4.3.) > Register a memory address range with the userfaultfd object. > -- > 2.42.0.655.g421f12c284-goog >
diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 index e68085262..82aee667c 100644 --- a/man2/ioctl_userfaultfd.2 +++ b/man2/ioctl_userfaultfd.2 @@ -272,6 +272,14 @@ operation returns 0 on success. On error, \-1 is returned and .I errno is set to indicate the error. +If an error occurs, +the kernel may zero the provided +.I uffdio_api +structure. +The caller should treat its contents as unspecified, +and reinitialize it before re-attempting another +.B UFFDIO_API +call. Possible errors include: .TP .B EFAULT @@ -305,14 +313,6 @@ feature was enabled, but the calling process doesn't have the .B CAP_SYS_PTRACE capability. -.\" FIXME In the above error case, the returned 'uffdio_api' structure is -.\" zeroed out. Why is this done? This should be explained in the manual page. -.\" -.\" Mike Rapoport: -.\" In my understanding the uffdio_api -.\" structure is zeroed to allow the caller -.\" to distinguish the reasons for -EINVAL. -.\" .SS UFFDIO_REGISTER (Since Linux 4.3.) Register a memory address range with the userfaultfd object.