kern/86655

[Maxim Konovalov]

The following reply was made to PR kern/86655; it has been noted by GNATS.

From: Maxim Konovalov <maxim at macomnet.ru>
To: Micah <micahjon at ywave.com>
Cc: bug-followup at freebsd.org, mato <gamato at users.sourceforge.net>
Subject: Re: kern/86655
Date: Sun, 26 Nov 2006 21:36:57 +0300 (MSK)

 On Sun, 26 Nov 2006, 10:25-0800, Micah wrote:
 
 > Maxim Konovalov wrote:
 > > Hi Micah,
 > >
 > > I failed to see how your patch changes dos2unixchr() code path.  It
 > > seems it does the same things for any combinations of LCASE_* flags.
 > > Perhaps I'm just blind.  Could you explain your patch further?
 > >
 > > --
 > > Maxim Konovalov
 >
 > Oh, it's been a while, let me examine it...
 >
 > In dos2unixfn, lower comes from direntry.deLowerCase. deLowerCase is
 > byte 0x0c in the FAT dir entry that has two flags. One flag (bit 3)
 > determines the "case" of the 8 character filename, the other flag
 > (bit 4) determines the "case" of the 3 character extension.
 > Wikipedia has a good summary of this:
 > http://en.wikipedia.org/wiki/File_Allocation_Table#Directory_table
 >
 > Now for the code path: dos2unixchr will convert to lower case if
 > LCASE_BASE or LCASE_EXT or both are set. But dos2unixfn uses
 > dos2unixchr separately for the basename and the extension. So if
 > either LCASE_BASE or LCASE_EXT is set, dos2unixfn will convert both
 > the basename and extension to lowercase because it is blindly
 > passing in the state of both flags to dos2unixchr. The bit masks I
 > used ensure that only the state of LCASE_BASE gets passed to
 > dos2unixchr when the basename is converted, and only the state of
 > LCASE_EXT is passed in when the extension is converted.
 >
 > Here's an example run:
 >
 > In the original:
 > dosfn=TEST.TXT
 > lower=LCASE_EXT (meaning the filename should be TEST.txt)
 > unixfn=""
 > When dos2unixfn executes the first call to dos2unixchr, dos2unixchr will see
 > that LCASE_EXT is set and convert the basename to lowercase:
 > unixfn="test"
 > When dos2unixfn executes the second call to dos2unixchr, dos2unixchr will see
 > that LCASE_EXT is set and convert the extension to lowercase:
 > unixfn="test.txt" != "TEST.txt"
 >
 > In the patch:
 > dosfn=TEST.TXT
 > lower=LCASE_EXT (meaning the filename should be TEST.txt)
 > unixfn=""
 > When dos2unixfn executes the first call to dos2unixchr, dos2unixfn will mask
 > out all bits of lower but LCASE_BASE, dos2unixchr will see that no bits are
 > set and leave the basename as uppercase:
 > unixfn="TEST"
 > When dos2unixfn executes the second call to dos2unixchr, dos2unixfn will mask
 > out all bits of lower but LCASE_EXT, dos2unixchr will see that LCASE_EXT is
 > set and convert the extension to lowercase:
 > unixfn="TEST.txt" == "TEST.txt"
 >
 > Does that help, or did I miss something completely when I wrote the
 > patch?
 
 Yes, everything is clear now.  Thanks, Micah!
 
 -- 
 Maxim Konovalov