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Date: Wed, 23 Apr 2014 20:38:59 +0100
From: Filipe David Manana <fdmanana@...il.com>
To: "J S, Ajesh" <ajesh.js@...com>
Cc: "clm@...com" <clm@...com>, "jbacik@...com" <jbacik@...com>,
"linux-btrfs@...r.kernel.org" <linux-btrfs@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 001/001] btrfs: Mechanism to modify the permission of a subvolume
On Wed, Apr 23, 2014 at 2:28 PM, J S, Ajesh <ajesh.js@...com> wrote:
> From: Ajesh JS <ajesh.js@...com>
>
> This patch provides a mechanism to modify the permission of a subvolume in a btrfs file system
> This helps to apply a policy of having read-write subvolume inside a read-only subvolume.
> One use case is to have the whole root file system as a read-only subvolume and have /etc as a read-write subvolume inside.
Hi,
Why doesn't the existing properties feature (3.14) work for you?
Example:
$ mkfs.btrfs -f /dev/sdd
$ mount /dev/sdd /mnt/sdd
$ btrfs subvolume create /mnt/sdd/topsubvol
$ btrfs subvolume create /mnt/sdd/topsubvol/child
$ btrfs property set /mnt/sdd/topsubvol ro true
$ touch /mnt/sdd/topsubvol/file
$ touch: cannot touch ‘/mnt/sdd/topsubvol/file’: Read-only file system
$ touch /mnt/sdd/topsubvol/child/file
The property set/get just uses the ioctls BTRFS_IOC_SUBVOL_SETFLAGS
and BTRFS_IOC_SUBVOL_GETFLAGS.
thanks
>
> Signed-off-by: Ajesh JS <ajesh.js@...com>
> Reviewed-by: Liverance Fletcher <fletch@...com>; Clemenceau, <Matthieu matthieu.clemenceau@...com>
> "-------------------------------------------------------------------------"
> diff -rup linux-3.13.6/fs/btrfs/ioctl.c linux-3.13.6_btrfs/fs/btrfs/ioctl.c
> --- linux-3.13.6/fs/btrfs/ioctl.c 2014-03-07 11:37:02.000000000 +0530
> +++ linux-3.13.6_btrfs/fs/btrfs/ioctl.c 2014-03-19 14:25:28.375139699 +0530
> @@ -1636,6 +1636,68 @@ out:
> return ret;
> }
>
> +static noinline int btrfs_ioctl_subvol_modify(struct file *file,
> + void __user *arg)
> +{
> + struct btrfs_ioctl_vol_args_v2 *vol_args;
> + struct inode *inode = file_inode(file);
> + struct btrfs_root *root = BTRFS_I(inode)->root;
> + struct btrfs_trans_handle *trans;
> + u64 root_flags;
> + u64 flags;
> + int ret = 0;
> +
> + ret = mnt_want_write_file(file);
> + if (ret)
> + goto out;
> +
> + if (btrfs_ino(inode) != BTRFS_FIRST_FREE_OBJECTID) {
> + ret = -EINVAL;
> + goto out_drop_write;
> + }
> + vol_args = memdup_user(arg, sizeof(*vol_args));
> + if (IS_ERR(vol_args))
> + goto out_drop_write;
> + vol_args->name[BTRFS_SUBVOL_NAME_MAX] = '\0';
> + flags = vol_args->flags;
> + if (!inode_owner_or_capable(inode)) {
> + ret = -EACCES;
> + goto out_drop_write;
> + }
> +
> + down_write(&root->fs_info->subvol_sem);
> + root_flags = btrfs_root_flags(&root->root_item);
> +
> + if (flags & BTRFS_SUBVOL_RDONLY) {
> + btrfs_set_root_flags(&root->root_item,
> + root_flags | BTRFS_ROOT_SUBVOL_RDONLY);
> + printk(KERN_INFO "Setting %s to ro\n", vol_args->name);
> + } else {
> + btrfs_set_root_flags(&root->root_item,
> + root_flags & ~BTRFS_ROOT_SUBVOL_RDONLY);
> + printk(KERN_INFO "Setting %s to rw\n", vol_args->name);
> + }
> +
> + trans = btrfs_start_transaction(root, 1);
> + if (IS_ERR(trans)) {
> + ret = PTR_ERR(trans);
> + goto out_reset;
> + }
> +
> + ret = btrfs_update_root(trans, root->fs_info->tree_root,
> + &root->root_key, &root->root_item);
> + btrfs_commit_transaction(trans, root);
> +
> +out_reset:
> + if (ret)
> + btrfs_set_root_flags(&root->root_item, root_flags);
> + up_write(&root->fs_info->subvol_sem);
> +out_drop_write:
> + mnt_drop_write_file(file);
> +out:
> + return ret;
> +}
> +
> static noinline int btrfs_ioctl_subvol_getflags(struct file *file,
> void __user *arg)
> {
> @@ -4509,6 +4571,8 @@ long btrfs_ioctl(struct file *file, unsi
> return btrfs_ioctl_snap_create(file, argp, 1);
> case BTRFS_IOC_SUBVOL_CREATE_V2:
> return btrfs_ioctl_snap_create_v2(file, argp, 1);
> + case BTRFS_IOC_SUBVOL_MODIFY:
> + return btrfs_ioctl_subvol_modify(file, argp);
> case BTRFS_IOC_SNAP_DESTROY:
> return btrfs_ioctl_snap_destroy(file, argp);
> case BTRFS_IOC_SUBVOL_GETFLAGS:
> diff -rup linux-3.13.6/include/uapi/linux/btrfs.h linux-3.13.6_btrfs/include/uapi/linux/btrfs.h
> --- linux-3.13.6/include/uapi/linux/btrfs.h 2014-03-07 11:37:02.000000000 +0530
> +++ linux-3.13.6_btrfs/include/uapi/linux/btrfs.h 2014-03-19 15:34:30.648255239 +0530
> @@ -606,5 +606,7 @@ static inline char *btrfs_err_str(enum b
> struct btrfs_ioctl_dev_replace_args)
> #define BTRFS_IOC_FILE_EXTENT_SAME _IOWR(BTRFS_IOCTL_MAGIC, 54, \
> struct btrfs_ioctl_same_args)
> +#define BTRFS_IOC_SUBVOL_MODIFY _IOW(BTRFS_IOCTL_MAGIC, 55, \
> + struct btrfs_ioctl_vol_args_v2)
>
> #endif /* _UAPI_LINUX_BTRFS_H */
> --
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--
Filipe David Manana,
"Reasonable men adapt themselves to the world.
Unreasonable men adapt the world to themselves.
That's why all progress depends on unreasonable men."
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