Re: execl bug?

From: Dan Nelson (dnelson_at_allantgroup.com)
Date: 12/30/04

  • Next message: Christopher Weimann: "Re: execl bug?" 
    Date: Wed, 29 Dec 2004 18:10:43 -0600
To: Christopher Weimann <csw@k12hq.com>

    In the last episode (Dec 29), Christopher Weimann said:
    > It seems that the open handle is carried through and usable by the
    > child program unless the parent has done something to move the file
    > pointer. For example the program below (tst.c) opens a file, reads a
    > line, rewinds then uses execl to call "cat -" which ought to send the
    > file to stdout.
    >
    > I thought I must be misunderstanding how execl is supposed to work so
    > I tried it on a Redhat box to see if everything behaves the same. It
    > doesn't. On Redhat the file is displayed just as I would expect.

    I think your problem here is with rewind(). There's nothing that says
    it has to change the underlying filedescriptor; FreeBSD's fseek code
    knows that the beginning of the file is still within its stdio buffer,
    so it simply resets the seek offset in the FILE* back to zero. See the
    code in /usr/src/lib/libc/stdio/fseek.c . Replacing your rewind() with
    an lseek(0,0,SEEK_SET) makes the program work.
      

    -- 
	Dan Nelson
	dnelson@allantgroup.com
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  • Next message: Christopher Weimann: "Re: execl bug?"

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