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Re: [RFC PATCH 3/4] xfs: add FREE_EOFBLOCKS ioctl

To: Brian Foster <bfoster@xxxxxxxxxx>
Subject: Re: [RFC PATCH 3/4] xfs: add FREE_EOFBLOCKS ioctl
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Mon, 3 Sep 2012 15:17:43 +1000
Cc: xfs@xxxxxxxxxxx
In-reply-to: <1346097111-4476-4-git-send-email-bfoster@xxxxxxxxxx>
References: <1346097111-4476-1-git-send-email-bfoster@xxxxxxxxxx> <1346097111-4476-4-git-send-email-bfoster@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Mon, Aug 27, 2012 at 03:51:50PM -0400, Brian Foster wrote:
> The XFS_IOC_FREE_EOFBLOCKS ioctl allows users to invoke an EOFBLOCKS
> scan. The xfs_eofblocks structure is defined to support the command
> parameters (quota type/id and minimum file size).
> 
> Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
> ---
>  fs/xfs/xfs_fs.h       |   10 ++++++++++
>  fs/xfs/xfs_ioctl.c    |   25 +++++++++++++++++++++++++
>  fs/xfs/xfs_quota.h    |    1 +
>  fs/xfs/xfs_quotaops.c |    2 +-
>  4 files changed, 37 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/xfs/xfs_fs.h b/fs/xfs/xfs_fs.h
> index c13fed8..6f93db9 100644
> --- a/fs/xfs/xfs_fs.h
> +++ b/fs/xfs/xfs_fs.h
> @@ -339,6 +339,15 @@ typedef struct xfs_error_injection {
>  
>  
>  /*
> + * Speculative preallocation trimming.
> + */
> +typedef struct xfs_eofblocks {
> +     __u32           id;             /* quota id */
> +     __u32           qtype;          /* quota type */
> +     __u64           min_file_size;  /* minimum file size */
> +} xfs_eofblocks_t;

No typedefs.

Additionally: this is a user facing API for functionality that has
wider potential use than quota. For example, xfs_fsr runs out of
space in an AG, but it really wants to put a file there, so it calls
XFS_IOC_FREE_EOFBLOCKS to specify the AG it wants all the prealloc
removed from.

So, the structure needs a version number so the kernel knows what
fields the application is aware of, a flags field to say what
operation is being done (i.e. flush by projid) rather than a "qtype"
and a bunch of padding so that we can add new elements to it as need
arises without breaking existing user binaries.

>   * ioctl commands that replace IRIX syssgi()'s
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 0e0232c..b91cbcd 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1602,6 +1602,31 @@ xfs_file_ioctl(
>               error = xfs_errortag_clearall(mp, 1);
>               return -error;
>  
> +     case XFS_IOC_FREE_EOFBLOCKS: {
> +             struct xfs_eofblocks eofb;
> +             int qtype;
> +
> +             if (copy_from_user(&eofb, arg, sizeof(eofb)))
> +                     return -XFS_ERROR(EFAULT);
> +
> +             qtype = xfs_quota_type(eofb.qtype);
> +
> +             /*
> +              * TODO: The filtering code currently uses the id in the inode.
> +              * Therefore, I don't think it really matters whether the
> +              * particular quota type is enabled (and the dquot is attached).
> +              *
> +              * Alternatively, we could filter by dquot type. This would
> +              * mean we might have to make sure dquot's are attached during
> +              * the scan and that the particular quota type is enabled. I'm
> +              * not sure that this buys us anything.
> +              */

If quota is not enabled, then a request to free blocks determined by
a quota ID is invalid and should be rejected. It's a user API - what
is and isn't supported needs to be written down in black and white
(i.e. in the xfsctl man page).

> +             /* TODO: might want to just use the eofb structure here */
> +             error = xfs_inodes_free_eofblocks(mp, qtype, eofb.id, 
> eofb.min_file_size, EOFBLOCKS_WAIT);

Yes, just pass the structure - it means it can be passed all the way
down to the execute function, and only that code needs to handle
different versions of the structure.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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