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To: Julian Elischer <julian@whistle.com>
Subject: Re: sb being written to r/o disks. 
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In-reply-to: Your message of "Tue, 03 Feb 1998 16:30:41 PST."
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Date: Tue, 03 Feb 1998 16:44:05 -0800
From: Kirk McKusick <mckusick@McKusick.COM>
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	Sender: julian@whistle.com
	Date: Tue, 03 Feb 1998 16:30:41 -0800
	From: Julian Elischer <julian@whistle.com>
	Organization: Whistle Communications
	To: mckusick@mckusick.com, current@freebsd.org
	Subject: sb being written to r/o disks.

	hmmmm it's amazing what new debugging info brings to light!
	I noticed this with the mount from the soft-updates integration.
	notice the two extra fields in 'mount'.

	# mount
	/dev/wd0e on / (local, read-only, writes: sync 4 async 0)
	/dev/wd0h on /data (local, softdep, writes: sync 2 async 0)
	/dev/wd0g on /var (local, writes: sync 2 async 0)
	procfs on /proc (local, writes: sync 0 async 0)


	something is doing syncronous writes to a r/o FS..
	who? that's easy..

	# mount -u -ordonly /
	Breakpoint at   _mount: pushl   %ebp
	db> b bwrite
	db> c
	Breakpoint at   _bwrite:        pushl   %ebp
	db> tr
	_bwrite(f245ccf4,0) at _bwrite
	_ffs_sbupdate(f045f200,1) at _ffs_sbupdate+0xb0
	_ffs_mount(f045fc00,efbfd268,efbfd1cc,f3666eb8,f364e740) at
	_ffs_mount+0x1e5
	_mount(f364e740,f3666f94,0,efbfd268,1201) at _mount+0x416
	_syscall(27,27,1201,efbfd268,efbfd238) at _syscall+0x187
	_Xsyscall() at _Xsyscall+0x35
	--- syscall 0x15, eip = 0x6a95, esp = 0xefbfd188, ebp = 0xefbfd238 ---
	db> 

	apparently _ffs_sbupdate() doesn't know to check if the fs is readonly..

	julian

If you are doing a downgrade from r/w to r/o then the update is
correct. If it is r/o to r/o then it is definitely a bug.

	~Kirk