[Bug 254333] [tcp] sysctl net.inet.tcp.hostcache.list hangs

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254333

--- Comment #37 from commit-hook at FreeBSD.org ---
A commit in branch stable/12 references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=54beb1ef2c831394ef908ef52bac690a4fe362e0

commit 54beb1ef2c831394ef908ef52bac690a4fe362e0
Author:     Richard Scheffenegger <rscheff at FreeBSD.org>
AuthorDate: 2021-03-28 21:12:03 +0000
Commit:     Richard Scheffenegger <rscheff at FreeBSD.org>
CommitDate: 2021-04-16 20:51:57 +0000

    tcp: reduce memory footprint when listing tcp hostcache

    In tcp_hostcache_list, the sbuf used would need a large (~2MB)
    blocking allocation of memory (M_WAITOK), when listing a
    full hostcache. This may stall the requestor for an indeterminate
    time.

    A further optimization is to return the expected userspace
    buffersize right away, rather than preparing the output of
    each current entry of the hostcase, provided by: @tuexen.

    This makes use of the ready-made functions of sbuf to work
    with sysctl, and repeatedly drain the much smaller buffer.

    PR: 254333
    MFC after: 2 weeks
    Reviewed By: #transport, tuexen
    Sponsored by: NetApp, Inc.
    Differential Revision: https://reviews.freebsd.org/D29471

    (cherry picked from commit cb0dd7e122b8936ad61a141e65ef8ef874bfebe5)

 sys/netinet/tcp_hostcache.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

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