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Re: kern/54470: Adapt FFS to work with HP-UX UFS1 variant

Do we have a way to construct a file system that works with NetBSD, which has a physical sector size other than DEV_BSIZE?  If so, I can test against it.

Note too that the macros in question exist only within the scope of the fsck_ffs utility.  The other userland programs that I adapted didn't need them, and the kernel uses macros that depend on struct ump and could easily be special-cased for HP-UX or other old file systems if need be.  Come to think of it, in fsck_ffs we could just do something like

    exter daddr_t dev_bshift;

    daddr_t dev_bshift = DEV_BSHIFT;

    #define BTODB(size) ((size) >> dev_bshift)
    #define DBTOB(size) ((size) << dev_bshift)

and change the value of dev_bsize, if necessary, in the setup.  The kernel would do the same, but storing the dev_bshift value in struct ump.  Would this address your concern?



On 8/17/2019 4:20 AM, Michael van Elst wrote:
The following reply was made to PR kern/54470; it has been noted by GNATS.

From: (Michael van Elst)
Subject: Re: kern/54470: Adapt FFS to work with HP-UX UFS1 variant
Date: Sat, 17 Aug 2019 11:15:28 -0000 (UTC) (Konrad Schroder) writes:
>Can you be more specific?  It gives the right values for my HP-UX image,
  >and for existing NetBSD file systems.
>> >+#define BTODB(fs, size) ((size) >> ((fs)->fs_fshift - (fs)->fs_fsbtodb))
  >>   >+#define DBTOB(fs, bc)   ((bc) << ((fs)->fs_fshift - (fs)->fs_fsbtodb))
The original BSD code used definitions like these above as a 'disk offset'
  referred to physical block numbers. This is still used that way in
NetBSD disk drivers always use logical block numbers for a block size
  of 512 bytes (DEV_BSIZE) and filesystems ignore the superblock values when
  translating between filesystem block numbers and disk block numbers.
For FFS the macros FFS_FSBTODB / FFS_DBTOFSB are used to do this conversion.
  They are differently defined for kernel and userland to address the different
btodb / dbtob are originally MD macros (then unified) that always used
  a platform specific unit, i.e. DEV_BSIZE, to specify disk offsets. This
  unit is independent of a particular filesystem and the physical blocks of
  a specific device.
Now what unit does di_blocks use, it's only used for reporting and quota
  calculations ? The original code used btodb(file_length), i.e. the values
  used the platform-wide DEV_BSIZE as a unit and that's what we still use
Your patch changes that and di_blocks is now using the physical block
  size of the particular disk (recorded in the superblock) as the unit.
  Apparently that's what HP-UX is doing.
I see two issues: you added another view on disk offsets and you break
  existing filesystems that use a physical sector size != 512.
Apparently we need conditional code to handle di_blocks for the
  different systems.
                                  Michael van Elst
                                  "A potential Snark may lurk in every tree."

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