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    SubjectRe: seq_file and exporting dynamically allocated data
    On Mon, Nov 17, 2003 at 08:38:24AM +0000, Tigran Aivazian wrote:
    > The reason why I didn't use pread(2) is because I have to do multiple
    > calls to read(2). There is no way that I know of to pack more than a
    > single page into a single read(2) with seq_file API.

    Well, one way to do it is to say that if you don't get a short read,
    then the file is longer.


    On Mon, Nov 17, 2003 at 08:38:24AM +0000, Tigran Aivazian wrote:
    > Yes, I remember Al saying "it's not a page" but in practice it still
    > appears to be limited to a page unless someone shows a sample seq_file
    > module which can provide more than a page of data on a single read(2). The
    > implementations I have looked at in the kernel (e.g. mm/slab.c) are
    > limited to a single page per read(2).

    There's a retry loop where the buffer size is doubled each iteration
    that looks to me like automagic sizing in the code for seq_read(). I
    can't say I've actually tried to rely on getting more than a page
    at a time through seq_read(), though.


    -- wli


    The retry loop:

    while (1) {
    pos = m->index;
    p = m->op->start(m, &pos);
    err = PTR_ERR(p);
    if (!p || IS_ERR(p))
    break;
    err = m->op->show(m, p);
    if (err)
    break;
    if (m->count < m->size)
    goto Fill;
    m->op->stop(m, p);
    kfree(m->buf);
    m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
    if (!m->buf)
    goto Enomem;
    m->count = 0;
    }
    -
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