[PATCH v2] quotactl.2: Add some details about Q_QUOTAON

[Yang Xu <xuyang2018.jy@cn.fujitsu.com>]

For Q_QUOTAON, on old kernel we can use quotacheck -ug to
generate quota files. But in current kernel, we can also hide them
in system inodes and indicate them by using "quota" or project feature.

For user or group quota, we can do as below(etc ext4):
mkfs.ext4 -F -o quota /dev/sda5
mount /dev/sda5 /mnt
quotactl(QCMD(Q_QUOTAON, USRQUOTA), /dev/sda5, QFMT_VFS_V0, NULL);

For project quota, we can do as below(etc ext4)
mkfs.ext4 -F -o quota,project /dev/sda5
mount /dev/sda5 /mnt
quotactl(QCMD(Q_QUOTAON, PRJQUOTA), /dev/sda5, QFMT_VFS_V0, NULL);

Signed-off-by: Yang Xu <xuyang2018.jy@cn.fujitsu.com>
---
 man2/quotactl.2 | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/man2/quotactl.2 b/man2/quotactl.2
index e0d40a2be..215ec6252 100644
--- a/man2/quotactl.2
+++ b/man2/quotactl.2
@@ -117,7 +117,15 @@ argument points to the pathname of a file containing the quotas for
 the filesystem.
 The quota file must exist; it is normally created with the
 .BR quotacheck (8)
-program.
+program. Quota information can be also stored in hidden system inodes
+for ext4, xfs and other filesystems if the filesystem is configured so.
+In this case, there are no visible quota files and there is no need to
+use
+.BR quotacheck (8).
+Quota information is always kept consistent by the filesystem and Q_QUOTAON
+quotactl only enables enforcement of quota limits. The presence of hidden
+system inodes with quota information is indicated by DQF_SYS_FILE flag in
+Q_GETINFO output.
 This operation requires privilege
 .RB ( CAP_SYS_ADMIN ).
 .TP 8
@@ -638,7 +646,8 @@ The
 .I id
 argument is ignored.
 .TP
-.B Q_XQUOTARM
+.B Q_XQUOTARM() " (since Linux 3.16)"
+.\" 9da93f9b7cdf8ab28da6b364cdc1fafc8670b4dc
 Free the disk space taken by disk quotas. The
 .I addr
 argument should be a pointer to an
-- 
2.18.0