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Re: bash-3.1-7 BUG

On Wed, Sep 13, 2006 at 04:38:33AM +0000, Eric Blake wrote:
>> At any rate, thanks for narrowing down your application
>> to a smaller test case; I'll see what I can find with it.
>Here's something interesting in the strace:
>   30  518741 [main] bash 2084 readv: readv (255, 0x22C060, 1) blocking, sigcatchers 1
>   30  518771 [main] bash 2084 readv: no need to call ready_for_read
>   34  518805 [main] bash 2084 fhandler_base::read: read 0 bytes ()
>   29  518834 [main] bash 2084 fhandler_base::read: returning 135, text mode
>   33 1682871 [main] bash 2084 fhandler_base::lseek: lseek (/home/eblake/text/, -103, 1)
>   32 1682903 [main] bash 2084 fhandler_base::lseek: setting file pointer to 429
>4967295 (high), 4294967193 (low)
>   34 1682937 [main] bash 2084 lseek64: 39 = lseek (255, -103, 1)
>Seems like a text mode lseek bug (no surprise there, since cgf
>predicted that there are still some corner cases).  The file is 142
>bytes, but has seven \r\n pairs, so the readv correctly returned 135
>characters read.  But the lseek back to the start of the third line
>temporarily set the file pointer to -3,

(actually -103, 4294967193U == -103)

>then settled on an offset of 39 (39 + 103 gives 142 bytes, as if in
>binary mode); the offset really should have been 32 characters in (byte
>34 is the start of the third line, so two \r would be skipped at that
>point).  I'm still not sure if it is bash's fault or cygwin's.  But the
>file definitely was read in text mode when it resided in a text mount.

Is bash assuming that it can read N characters and then subtract M
characters from the current position to get back to the beginning of a
line?  If so, hmm.  I guess this explains why it was reading a byte at a
time before.  It must be counting characters rather than calling lseek
to figure out where it is.

Fixing this is rarely as simple as just calling lseek, though, of


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