On Tue 28-01-20 11:06:31, Sascha Hauer wrote:
> Hi Jan,
>
> On Mon, Jan 27, 2020 at 11:45:18AM +0100, Jan Kara wrote:
> > > cmds = cmd >> SUBCMDSHIFT;
> > > type = cmd & SUBCMDMASK;
> > >
> > > +
> >
> > Unnecessary empty line added...
>
> Fixed
>
> > > + if (q_path) {
> > > + ret = user_path_at(AT_FDCWD, special,
> > > + LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> > > + &sb_path);
> > > + if (ret)
> > > + goto out;
> > > +
> > > + sb = sb_path.mnt->mnt_sb;
> >
> > So I've realized that just looking up superblock with user_path_at() is not
> > enough. Quota code also expects that the superblock will be locked
> > (sb->s_umount) and filesystem will not be frozen (in case the quota
> > operation is going to modify the filesystem). This is needed to serialize
> > e.g. remount and quota operations or quota operations among themselves.
> > So you still need something like following to get superblock from the path:
>
> Ok, here's an updated version. I'll send an update for the whole series
> when Richard had a look over it.
>
> Sascha
>
> ----------------------------8<-----------------------------
>
> From 9c91395f2667c8a48f52a80896e559daf16f4a4c Mon Sep 17 00:00:00 2001
> From: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> Date: Wed, 30 Oct 2019 08:35:11 +0100
> Subject: [PATCH] quota: Allow to pass mount path to quotactl
>
> This patch introduces the Q_PATH flag to the quotactl cmd argument.
> When given, the path given in the special argument to quotactl will
> be the mount path where the filesystem is mounted, instead of a path
> to the block device.
> This is necessary for filesystems which do not have a block device as
> backing store. Particularly this is done for upcoming UBIFS support.
>
> Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
Thanks. The patch looks good to me now. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> fs/quota/quota.c | 75 ++++++++++++++++++++++++++++++++------
> include/uapi/linux/quota.h | 1 +
> 2 files changed, 64 insertions(+), 12 deletions(-)
>
> diff --git a/fs/quota/quota.c b/fs/quota/quota.c
> index 5444d3c4d93f..712b71760f9d 100644
> --- a/fs/quota/quota.c
> +++ b/fs/quota/quota.c
> @@ -19,6 +19,7 @@
> #include <linux/types.h>
> #include <linux/writeback.h>
> #include <linux/nospec.h>
> +#include <linux/mount.h>
>
> static int check_quotactl_permission(struct super_block *sb, int type, int cmd,
> qid_t id)
> @@ -810,6 +811,36 @@ static struct super_block *quotactl_block(const char __user *special, int cmd)
> #endif
> }
>
> +static struct super_block *quotactl_path(const char __user *special, int cmd,
> + struct path *path)
> +{
> + struct super_block *sb;
> + int ret;
> +
> + ret = user_path_at(AT_FDCWD, special, LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> + path);
> + if (ret)
> + return ERR_PTR(ret);
> +
> + sb = path->mnt->mnt_sb;
> +restart:
> + if (quotactl_cmd_onoff(cmd))
> + down_write(&sb->s_umount);
> + else
> + down_read(&sb->s_umount);
> +
> + if (quotactl_cmd_write(cmd) && sb->s_writers.frozen != SB_UNFROZEN) {
> + if (quotactl_cmd_onoff(cmd))
> + up_write(&sb->s_umount);
> + else
> + up_read(&sb->s_umount);
> + wait_event(sb->s_writers.wait_unfrozen,
> + sb->s_writers.frozen == SB_UNFROZEN);
> + goto restart;
> + }
> +
> + return sb;
> +}
> /*
> * This is the system call interface. This communicates with
> * the user-level programs. Currently this only supports diskquota
> @@ -821,8 +852,9 @@ int kernel_quotactl(unsigned int cmd, const char __user *special,
> {
> uint cmds, type;
> struct super_block *sb = NULL;
> - struct path path, *pathp = NULL;
> + struct path file_path, *file_pathp = NULL, sb_path;
> int ret;
> + bool q_path;
>
> cmds = cmd >> SUBCMDSHIFT;
> type = cmd & SUBCMDMASK;
> @@ -830,6 +862,9 @@ int kernel_quotactl(unsigned int cmd, const char __user *special,
> if (type >= MAXQUOTAS)
> return -EINVAL;
>
> + q_path = cmds & Q_PATH;
> + cmds &= ~Q_PATH;
> +
> /*
> * As a special case Q_SYNC can be called without a specific device.
> * It will iterate all superblocks that have quota enabled and call
> @@ -847,28 +882,44 @@ int kernel_quotactl(unsigned int cmd, const char __user *special,
> * resolution (think about autofs) and thus deadlocks could arise.
> */
> if (cmds == Q_QUOTAON) {
> - ret = user_path_at(AT_FDCWD, addr, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
> + ret = user_path_at(AT_FDCWD, addr,
> + LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT,
> + &file_path);
> if (ret)
> - pathp = ERR_PTR(ret);
> + file_pathp = ERR_PTR(ret);
> else
> - pathp = &path;
> + file_pathp = &file_path;
> }
>
> - sb = quotactl_block(special, cmds);
> + if (q_path)
> + sb = quotactl_path(special, cmds, &sb_path);
> + else
> + sb = quotactl_block(special, cmds);
> +
> if (IS_ERR(sb)) {
> ret = PTR_ERR(sb);
> goto out;
> }
>
> - ret = do_quotactl(sb, type, cmds, id, addr, pathp);
> + ret = do_quotactl(sb, type, cmds, id, addr, file_pathp);
> +
> + if (q_path) {
> + if (quotactl_cmd_onoff(cmd))
> + up_write(&sb->s_umount);
> + else
> + up_read(&sb->s_umount);
> +
> + path_put(&sb_path);
> + } else {
> + if (!quotactl_cmd_onoff(cmds))
> + drop_super(sb);
> + else
> + drop_super_exclusive(sb);
> + }
>
> - if (!quotactl_cmd_onoff(cmds))
> - drop_super(sb);
> - else
> - drop_super_exclusive(sb);
> out:
> - if (pathp && !IS_ERR(pathp))
> - path_put(pathp);
> + if (file_pathp && !IS_ERR(file_pathp))
> + path_put(file_pathp);
> return ret;
> }
>
> diff --git a/include/uapi/linux/quota.h b/include/uapi/linux/quota.h
> index f17c9636a859..e1787c0df601 100644
> --- a/include/uapi/linux/quota.h
> +++ b/include/uapi/linux/quota.h
> @@ -71,6 +71,7 @@
> #define Q_GETQUOTA 0x800007 /* get user quota structure */
> #define Q_SETQUOTA 0x800008 /* set user quota structure */
> #define Q_GETNEXTQUOTA 0x800009 /* get disk limits and usage >= ID */
> +#define Q_PATH 0x400000 /* quotactl special arg contains mount path */
>
> /* Quota format type IDs */
> #define QFMT_VFS_OLD 1
> --
> 2.25.0
>
>
> --
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> Steuerwalder Str. 21 | http://www.pengutronix.de/ |
> 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
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--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
