[PATCH] Add manpage for get/set fsuuid ioctl.

[Jeremy Bongio <bongiojp@gmail.com>]

This manpage written for the case where xfs or other filesystems will
implement the same ioctl.

Signed-off-by: Jeremy Bongio <bongiojp@gmail.com>
---
 man2/ioctl_fsuuid.2 | 110 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 man2/ioctl_fsuuid.2

diff --git a/man2/ioctl_fsuuid.2 b/man2/ioctl_fsuuid.2
new file mode 100644
index 000000000..db414bf59
--- /dev/null
+++ b/man2/ioctl_fsuuid.2
@@ -0,0 +1,110 @@
+.\" Copyright (c) 2022 Google, Inc., written by Jeremy Bongio <bongiojp@gmail.com>
+.\"
+.\" SPDX-License-Identifier: GPL-2.0-or-later
+.TH IOCTL_FSUUID 2 2022-07-08 "Linux" "Linux Programmer's Manual"
+.SH NAME
+ioctl_fsuuid \- get or set a filesystem label
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.nf
+.BR "#include <linux/fs.h>" "      /* Definition of " *FSLABEL* " constants */"
+.BR "#include <uuid/uuid.h>" "     /* Definition of " *UUID_MAX* " constants */"
+.B #include <sys/ioctl.h>
+.PP
+.BI "int ioctl(int " fd ", FS_IOC_GETFSUUID, struct " fsuuid ");"
+.BI "int ioctl(int " fd ", FS_IOC_SETFSUUID, struct " fsuuid ");"
+.fi
+.SH DESCRIPTION
+If a filesystem supports online uuid manipulation, these
+.BR ioctl (2)
+operations can be used to get or set the uuid for the filesystem
+on which
+.I fd
+resides.
+.PP
+The
+.B FS_IOC_GETFSUUID
+operation will read the filesystem uuid into
+.I fu_uuid.
+.I fu_len
+must be set to the number of bytes allocated for the uuid.
+.I fu_uuid
+must be initialized to the size of the filesystem uuid.
+The maximmum number of bytes for a uuid is
+.BR UUID_MAX.
+.I fu_flags
+must be set to 0.
+.PP
+The
+.B FS_IOC_SETFSUUID
+operation will set the filesystem uuid according to
+.I fu_uuid.
+.I fu_len
+must be set to the number of bytes in the uuid.
+.I fu_flags
+must be set to 0. The
+.B FS_IOC_SETFSUUID
+operation requires privilege
+.RB ( CAP_SYS_ADMIN ).
+.PP
+This information is conveyed in a structure of
+the following form:
+.PP
+.in +4n
+.EX
+struct fsuuid {
+       __u32       fu_len;
+       __u32       fu_flags;
+       __u8        fu_uuid[];
+};
+.EE
+.in
+.PP
+.SH RETURN VALUE
+On success zero is returned.
+On error, \-1 is returned, and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+Possible errors include (but are not limited to) the following:
+.TP
+.B EFAULT
+Either the pointer to the
+.I fsuuid
+structure is invalid or
+.I fu_uuid
+has not been initialized properly.
+.TP
+.B EINVAL
+The specified arguments are invalid.
+.I fu_len
+does not match the filesystem uuid length or
+.I fu_flags
+has bits set that are not implemented.
+.TP
+.B ENOTTY
+The filesystem does not support the ioctl.
+.TP
+.B EOPNOTSUPP
+The filesystem does not currently support changing the uuid through this
+ioctl. This may be due to incompatible feature flags.
+.TP
+.B EPERM
+The calling process does not have sufficient permissions to set the uuid.
+.SH VERSIONS
+These
+.BR ioctl (2)
+operations first appeared in Linux 5.19.
+They were previously known as
+.B EXT4_IOC_GETFSUUID
+and
+.B EXT4_IOC_SETFSUUID
+and were private to ext4.
+.SH CONFORMING TO
+This API is Linux-specific.
+.BR UUID_MAX.
+.SH SEE ALSO
+.BR ioctl (2)
+
-- 
2.37.0.144.g8ac04bfd2-goog