Re: git: 460ed6106cf0 - main - Add support for managing UFS/FFS snapshots to fsck_ffs(8).

On Wed, Nov 09, 2022 at 06:46:51PM +0000, Kirk McKusick wrote:
> The branch main has been updated by mckusick:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=460ed6106cf0854caff62e4eeba8ffcd00ab0690
> 
> commit 460ed6106cf0854caff62e4eeba8ffcd00ab0690
> Author:     Kirk McKusick <mckusick@FreeBSD.org>
> AuthorDate: 2022-11-09 18:44:03 +0000
> Commit:     Kirk McKusick <mckusick@FreeBSD.org>
> CommitDate: 2022-11-09 18:46:31 +0000
> 
>     Add support for managing UFS/FFS snapshots to fsck_ffs(8).
>     
>     The kernel handles the managment of UFS/FFS snapshots. Since UFS/FFS
>     updates filesystem data (rather than always writing changes to new
>     locations like ZFS), the kernel must check every filesystem write
>     to see if the block being written is part of a snapshot. If it is
>     part of a snapshot, then the kernel must make a copy of the old
>     block value into a newly allocated block for the snapshot before
>     allowing the write to be done. Similarly, if a block is being freed,
>     the kernel must check to see if it is part of a snapshot and let
>     the snapshot claim the block rather than freeing it for future use.
>     When a snapshot is freed, its blocks need to be offered to older
>     snapshots and freed only if no older snapshots wish to claim them.
>     
>     When snapshots were added to UFS/FFS they were integrated into soft
>     updates and just a small part of the management of snapshots needed
>     to be added to fsck_ffs(8) as soft updates minimized the set of
>     snapshot changes that might need correction. When journaling was
>     added to soft updates a much more complete knowledge of snapshots
>     needed to be added to fsck_ffs(8) for it to be able to properly
>     handle the filesystem changes that a journal rollback needs to do
>     (specifically the freeing and allocation of blocks). Since this
>     functionality was unavailable, the use of snapshots was disabled
>     when running with journaled soft updates.
>     
>     This set of changes imports the kernel code for the management of
>     snapshots to fsck_ffs(8). With this code in place it will become
>     possible to enable snapshots when running with journalled soft
>     updates. The most immediate benefit will be the ability to use
>     snapshots to take consistent filesystem dumps on live filesystems.
>     Future work will be done to update fsck_ffs(8) to be able to use
>     snapshots to run in background on live filesystems running with
>     journaled soft updates.
>     

I think this broke the main build.

Notably:

% @@ -483,11 +507,38 @@ flush(int fd, struct bufarea *bp)
%                 }
%                 /* FALLTHROUGH */
%         default:
% +               copyonwrite(&sblock, bp, std_checkblkavail);
%                 blwrite(fd, bp->b_un.b_buf, bp->b_bno, bp->b_size);
%                 break;

https://ci.freebsd.org/job/FreeBSD-main-i386-build/24590/console

Glen