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ioctl_userfaultfd.2: Improve the UFFDIO_API description 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2017-01-04 16:40:19 +13:00
parent 405513d327
commit 9a3c219414
1 changed files with 42 additions and 7 deletions
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49
man2/ioctl_userfaultfd.2
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@ -94,17 +94,46 @@ struct uffdio_api {
The
.I api
field denotes the API version requested by the application.
The kernel verifies that it can support the requested version, and sets the
Before the call, the
.I features
field must be initialized to zero.
.\" FIXME Why must the 'features' field be initialized to zero?
The kernel verifies that it can support the requested API version,
and sets the
.I features
and
.I ioctls
fields to bit masks representing all the available features and the generic
.BR ioctl (2)
operations available.
.\" FIXME We need to say more about the list of bits that can appear in
.\" these two fields.
Currently, zero (i.e., no feature bits) is placed in the
.I features
field.
The returned
.I ioctls
field can contain the following bits:
.\" FIXME This user-space API seems not fully polished. Why are there
.\" not constants defined for each of the bit-mask values listed here?
.TP
.B 1 << _UFFDIO_API
The
.B UFFDIO_API
operation is supported.
.TP
.B 1 << _UFFDIO_REGISTER
The
.B UFFDIO_REGISTER
operation is supported.
.TP
.B 1 << _UFFDIO_UNREGISTER
The
.B UFFDIO_UNREGISTER
operation is supported.
.\" FIXME Is the above description of the 'ioctls' field correct.
.\" Does more need to be said?
.\"
.PP
This
.BR ioctl (2)
operation returns 0 on success.
@ -112,6 +141,8 @@ On error, \-1 is returned and
.I errno
is set to indicate the cause of the error.
Possible errors include:
.\" FIXME Is the following error list correct?
.\"
.TP
.B EINVAL
The userfaultfd has already been enabled by a previous
@ -119,9 +150,13 @@ The userfaultfd has already been enabled by a previous
operation.
.TP
.B EINVAL
The
.B UFFDIO_API
operation has already been performed on this userfaultfd file descriptor.
The API version requested in the
.I api
field is not supported by this kernel, or the
.I features
field was not zero.
.\" FIXME In this error case, the returned 'uffdio_api' structure
.\" zeroed out. Why is this done?
.\"
.SS UFFDIO_REGISTER
Register a memory address range with the userfaultfd object.