Re: [PATCH 7/9] man: create a separate RESBLKS ioctl manpage

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Jul 05, 2019 at 11:02:40AM -0500, Eric Sandeen wrote:
> On 6/20/19 11:51 AM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > Create a separate manual page for the xfs RESBLKS ioctls so we can
> > document how it works.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >  man/man2/ioctl_xfs_getresblks.2 |   65 +++++++++++++++++++++++++++++++++++++++
> >  man/man2/ioctl_xfs_setresblks.2 |    1 +
> >  man/man3/xfsctl.3               |   14 +++++++-
> >  3 files changed, 78 insertions(+), 2 deletions(-)
> >  create mode 100644 man/man2/ioctl_xfs_getresblks.2
> >  create mode 100644 man/man2/ioctl_xfs_setresblks.2
> > 
> > 
> > diff --git a/man/man2/ioctl_xfs_getresblks.2 b/man/man2/ioctl_xfs_getresblks.2
> > new file mode 100644
> > index 00000000..694b4496
> > --- /dev/null
> > +++ b/man/man2/ioctl_xfs_getresblks.2
> > @@ -0,0 +1,65 @@
> > +.\" Copyright (c) 2019, Oracle.  All rights reserved.
> > +.\"
> > +.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
> > +.\" SPDX-License-Identifier: GPL-2.0+
> > +.\" %%%LICENSE_END
> > +.TH IOCTL-XFS-GETRESBLKS 2 2019-06-17 "XFS"
> > +.SH NAME
> > +ioctl_xfs_getresblks \- query XFS summary counter information
>                                      ^^^^^^^^^^^^^^^
> 
> "query and set XFS free space reservation information"

DOH.

Yes, thanks for fixing that. :)

> > +.SH SYNOPSIS
> > +.br
> > +.B #include <xfs/xfs_fs.h>
> > +.PP
> > +.BI "int ioctl(int " fd ", XFS_IOC_GET_RESBLKS, struct xfs_fsop_resblks *" arg );
> > +.br
> > +.BI "int ioctl(int " fd ", XFS_IOC_SET_RESBLKS, struct xfs_fsop_resblks *" arg );
> > +.SH DESCRIPTION
> 
> I wonder if starting with a "don't use" right here would be wise, something like:
> 
> "Note: This is a[n] test/debug ioctl intended only for use by XFS filesystem developers."

I'm partial to "This is an extraordinary way to eat your data!" :)

But yes it should have a warning label for SET_RESBLKS.

--D

> > +Query or set the free space reservation information.
> > +These blocks are reserved by the filesystem as a final attempt to prevent
> > +metadata update failures due to insufficient space.
> > +Only the system administrator can call these ioctls, because overriding the
> > +defaults is extremely dangerous and should never be tried by anyone.
> > +.PP
> > +The reservation information is conveyed in a structure of the following form:
> > +.PP
> > +.in +4n
> > +.nf
> > +struct xfs_fsop_resblks {
> > +	__u64  resblks;
> > +	__u64  resblks_avail;
> > +};
> > +.fi
> > +.in
> > +.PP
> > +.I resblks
> > +is the number of blocks that the filesystem will try to maintain to prevent
> > +critical out of space situations.
> > +.PP
> > +.I resblks_avail
> > +is the number of reserved blocks remaining.
> > +.SH RETURN VALUE
> > +On error, \-1 is returned, and
> > +.I errno
> > +is set to indicate the error.
> > +.PP
> > +.SH ERRORS
> > +Error codes can be one of, but are not limited to, the following:
> > +.TP
> > +.B EFSBADCRC
> > +Metadata checksum validation failed while performing the query.
> > +.TP
> > +.B EFSCORRUPTED
> > +Metadata corruption was encountered while performing the query.
> > +.TP
> > +.B EINVAL
> > +The specified allocation group number is not valid for this filesystem.
> > +.TP
> > +.B EIO
> > +An I/O error was encountered while performing the query.
> > +.TP
> > +.B EPERM
> > +Caller does not have permission to call this ioctl.
> > +.SH CONFORMING TO
> > +This API is specific to XFS filesystem on the Linux kernel.
> > +.SH SEE ALSO
> > +.BR ioctl (2)
> > diff --git a/man/man2/ioctl_xfs_setresblks.2 b/man/man2/ioctl_xfs_setresblks.2
> > new file mode 100644
> > index 00000000..209bc0a8
> > --- /dev/null
> > +++ b/man/man2/ioctl_xfs_setresblks.2
> > @@ -0,0 +1 @@
> > +.so man2/ioctl_xfs_getresblks.2
> > diff --git a/man/man3/xfsctl.3 b/man/man3/xfsctl.3
> > index ee3188ec..89975a3c 100644
> > --- a/man/man3/xfsctl.3
> > +++ b/man/man3/xfsctl.3
> > @@ -396,12 +396,21 @@ See
> >  .BR ioctl_xfs_fscounts (2)
> >  for more information.
> >  
> > +.TP
> > +.nf
> > +.B XFS_IOC_GET_RESBLKS
> > +.fi
> > +.TP
> > +.B XFS_IOC_SET_RESBLKS
> > +See
> > +.BR ioctl_xfs_getresblks (2)
> > +for more information.
> > +Save yourself a lot of frustration and avoid these ioctls.
> > +
> >  .PP
> >  .nf
> >  .B XFS_IOC_THAW
> >  .B XFS_IOC_FREEZE
> > -.B XFS_IOC_GET_RESBLKS
> > -.B XFS_IOC_SET_RESBLKS
> >  .B XFS_IOC_FSGROWFSDATA
> >  .B XFS_IOC_FSGROWFSLOG
> >  .fi
> > @@ -419,6 +428,7 @@ as they are not of general use to applications.
> >  .BR ioctl_xfs_scrub_metadata (2),
> >  .BR ioctl_xfs_fsinumbers (2),
> >  .BR ioctl_xfs_fscounts (2),
> > +.BR ioctl_xfs_getresblks (2),
> >  .BR fstatfs (2),
> >  .BR statfs (2),
> >  .BR xfs (5),
> >