[PATCH 0/6] tools/libxs: Fix SIGPIPE handling issues

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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

 tools/libs/store/xs.c | 394 +++++++++++++++++++++++++++---------------
 1 file changed, 258 insertions(+), 136 deletions(-)

-- 
2.39.2