On Fri, Jun 21, 2013 at 03:32:28PM +0800, Anand Jain wrote:
> btrfs-progs has to read fs info from the kernel to
> read the latest info instead of reading it from the disks,
> which generally is a stale info after certain critical
> operation.
>
> getting used_bytes parameter will help to fix
> btrfs filesystem show --kernel
> to show the current info of the fs
>
> v2->v3:
> everything is changed dropped the plan to introduce
> the new ioctl, as of now filesystem show could
> manage if we add the used_bytes parameter to the
> BTRFS_IOC_FS_INFO and
> Update the title from
> add framework to read fs info and dev info from the kernel
>
> Signed-off-by: Anand Jain <anand.j...@oracle.com>
> ---
> fs/btrfs/ioctl.c | 16 ++++++++++++++--
> include/uapi/linux/btrfs.h | 3 ++-
> 2 files changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 0e7bcc5..082c9fc 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2384,7 +2384,10 @@ static long btrfs_ioctl_fs_info(struct btrfs_root
> *root, void __user *arg)
> struct btrfs_ioctl_fs_info_args *fi_args;
> struct btrfs_device *device;
> struct btrfs_device *next;
> - struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
> + struct btrfs_fs_info *info = root->fs_info;
> + struct btrfs_fs_devices *fs_devices = info->fs_devices;
> + struct btrfs_space_info *si;
> + u64 used_bytes = 0;
> int ret = 0;
>
> if (!capable(CAP_SYS_ADMIN))
> @@ -2394,8 +2397,17 @@ static long btrfs_ioctl_fs_info(struct btrfs_root
> *root, void __user *arg)
> if (!fi_args)
> return -ENOMEM;
>
> + rcu_read_lock();
> + list_for_each_entry_rcu(si, &info->space_info, list) {
> + used_bytes += si->bytes_used + si->bytes_reserved
> + + si->bytes_pinned + si->bytes_readonly
> + + si->bytes_may_use;
> + }
> + rcu_read_unlock();
> + fi_args->used_bytes = used_bytes;
> +
So what exactly are we using this number for? ->bytes_may_used is going to
change all the damned time because of reservations and it could even make
used_bytes to appear to be larger than total_bytes because of overcommitting.
So why exactly do you want this value? Also how are you going to deal with
older kernels where this isn't populated? Thanks,
Josef
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