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    Subjectread() on relayfs channel returns premature 0
    Hi 

    I'm using relayfs to relay data from a kernel module to user space on
    a SuSE 2.6.5 kernel. I'm not absolutely sure what version of relayfs
    has been back ported to it.

    While reading data from the channel I've been seeing read() return 0
    prematurely. However, the 0 does not signify that the file is being
    closed for there is still data available afterwards.

    I've noticed that zeros occur when roughly one page of data has been
    read. I suspect that they occur whenever there is a read across the
    relayfs sub-buffers.

    Now I understand that this is not the latest release of relayfs (there
    are the redux patches, which I have yet to try). Nonetheless I'd like
    to know whether this behaviour is deliberate. Is it?

    Thanks,
    --
    Kingsley

    P.S. I've been able to get around this by deliberately modifying
    do_read() with the attached patch. I'm not absolutely sure its
    correct but it seems to work.
    Index: fs/relayfs/relay.c
    ===================================================================
    RCS file: /export/cvsroot/SuSE-Kernel-2.4.21/fs/relayfs/Attic/relay.c,v
    retrieving revision 1.1.2.1
    diff -u -r1.1.2.1 relay.c
    --- fs/relayfs/relay.c 18 Feb 2005 00:00:51 -0000 1.1.2.1
    +++ fs/relayfs/relay.c 23 Mar 2005 09:00:42 -0000
    @@ -1445,26 +1445,22 @@

    avail_offset = cur_idx = relay_get_offset(rchan, &max_offset);

    + last_buf_byte_offset = (read_bufno + 1) * buf_size - 1;
    if (cur_idx == read_offset) {
    if (atomic_read(&rchan->suspended) == 1) {
    - read_offset += 1;
    + read_offset = last_buf_byte_offset + 1;
    if (read_offset >= max_offset)
    read_offset = 0;
    *actual_read_offset = read_offset;
    } else {
    - *new_offset = read_offset;
    + *new_offset = read_offset;
    return 0;
    }
    - } else {
    - last_buf_byte_offset = (read_bufno + 1) * buf_size - 1;
    - if (read_offset == last_buf_byte_offset) {
    - if (unused_bytes != 1) {
    - read_offset += 1;
    - if (read_offset >= max_offset)
    - read_offset = 0;
    - *actual_read_offset = read_offset;
    - }
    - }
    + } else if ((read_offset + unused_bytes) > last_buf_byte_offset) {
    + read_offset = last_buf_byte_offset + 1;
    + if (read_offset >= max_offset)
    + read_offset = 0;
    + *actual_read_offset = read_offset;
    }

    read_bufno = read_offset / buf_size;
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