On 18.07.2024 18:48, Andrew Cooper wrote:
> While the purpose of this series is patch 6, it has a side effect of reducing
> the number of system calls substantally.
>
> Using a strace of test-xenstore as an example, we go from this:
>
> rt_sigaction(SIGPIPE, {sa_handler=SIG_IGN, sa_mask=[],
> sa_flags=SA_RESTORER, sa_restorer=0x7fda8278e2f0}, {sa_handler=SIG_DFL,
> sa_mask=[], sa_flags=SA_RESTORER, sa_restorer=0x7fda8278e2f0}, 8) = 0
> write(3, "\v\0\0\0\0\0\0\0\0\0\0\0\30\0\0\0", 16) = 16
> write(3, "xenstore-test/502673/a\0", 23) = 23
> write(3, "a", 1) = 1
> read(3, "\v\0\0\0\0\0\0\0\0\0\0\0\3\0\0\0", 16) = 16
> read(3, "OK\0", 3) = 3
> rt_sigaction(SIGPIPE, {sa_handler=SIG_DFL, sa_mask=[],
> sa_flags=SA_RESTORER, sa_restorer=0x7fda8278e2f0}, NULL, 8) = 0
>
> down to this:
>
> sendmsg(3, {msg_name=NULL, msg_namelen=0,
> msg_iov=[{iov_base="\v\0\0\0\0\0\0\0\0\0\0\0\30\0\0\0", iov_len=16},
> {iov_base="xenstore-test/504021/a\0", iov_len=23}, {iov_base="a",
> iov_len=1}], msg_iovlen=3, msg_controllen=0, msg_flags=0}, MSG_NOSIGNAL) = 40
> read(3, "\v\0\0\0\0\0\0\0\0\0\0\0\3\0\0\0", 16) = 16
> read(3, "OK\0", 3) = 3
>
>
> I.e., it removes 2x rt_sigaction(), and turns all write()'s into a single
> writev() or sendmsg().
>
>
> Reads are a little more problematic to deal with. Xenstored will produce a
> full package basically in one go, but libxenstore's reading is horrbly
> complicated by virtue of it being completely different depending on whether
> xs_watch() has created a secondary read thread or not.
>
> Andrew Cooper (6):
> tools/libxs: Fix length check in xs_talkv()
> tools/libxs: Rework xs_talkv() to take xsd_sockmsg within the iovec
> tools/libxs: Rationalise the definition of struct xs_handle
> tools/libxs: Track whether we're using a socket or file
> tools/libxs: Use writev()/sendmsg() instead of write()
> tools/libxs: Stop playing with SIGPIPE
The title of the entire series containing "Fix" vs there being no single
Fixes: tag throughout, afaics, leave unclear to me whether any or all of
this work wants/needs backporting. Please clarify.
Jan
