similar to: [libnbd] Simultaneous read and write

v1: https://www.redhat.com/archives/libguestfs/2019-June/msg00014.html I pushed a few bits which are uncontroversial. The main changes since v1 are: An extra patch removes the want_to_send / check for nbd_aio_is_ready in examples/threaded-reads-and-writes.c. This logic was wrong since commit 6af72b87 as was pointed out by Eric in his review. Comments and structure of

This works, but there's no time saving and I'm still investigating whether it does what I think it does. Nevertheless I thought I would post it because it (probably) implements the idea I had last night outlined in: https://www.redhat.com/archives/libguestfs/2019-June/msg00010.html The meat of the change is patch 4. Patch 5 is an example which I would probably fold into patch 4 for

While working on a new test of what happens when the server goes away while commands are in flight, I managed to hit a race where I hit death from SIGPIPE instead of a clean transition to the DEAD state. I also found myself wanting to use nbd_poll from the test, but with a way to distinguish between the state machine progressing vs. hanging. Eric Blake (2): socket: Avoid SIGPIPE where possible

This might not be the final solution, but it certainly seems to solve a deadlock for me that I could trigger by using 'nbdkit --filter=noparallel memory 512k' and calling nbd_aio_pread for a request larger than 256k (enough for the Linux kernel to block the server until libnbd read()s), immediately followed by nbd_aio_pwrite for a request larger than 256k (enough to block libnbd until the

On 5/31/19 11:01 AM, Richard W.M. Jones wrote: > This is a continuation of a discussion we were having on IRC. The > problems with IRC are it's not recorded and it's hard to have deep > technical conversations. I hope this is a decent summary. > > Problem simply stated: Certain NBD servers (qemu-nbd in particular) Also nbdkit for a plugin with

** NOT WORKING ** This patch shows how to integrate libnbd and the glib main loop. Posted mainly as a point of discussion as it doesn't quite work yet. Rich.

This is working now, and incorporates all of the changes in Eric's review, *except* that it still doesn't retire commands (although this seems to make no obvious difference, except possibly a performance and memory impact). Rich.

I fixed the deadlock - turned out to be an actual bug in the nbd plugin (see patch 8). I changed the command syntax so it's now: nbdkit nbd command=qemu arg=-f arg=qcow2 arg=/path/to/disk.qcow2 Nir wrote: 18:08 < nsoffer> rwmjones: regarding the nbd proxy patches, did you have specific flow that help us? 18:08 < nsoffer> rwmjones: or this is just a way to support qcow2 in the

On v1, we discussed whether cmds_to_issue needed to be a list, since it never had more than one element. I played with the idea of making it a list, and allowing the client to queue up new commands regardless of whether the state machine is currently in READY. I also polished up the tmp demo into a bit more full-fledged example file, worth including since it also let me discover a hard-to-hit race

Rich recently patched things to generate one man page per function rather than libnbd-api.3 (nice), but in doing so got stumped by a problem with a fresh git clone (automake fails for any 'include' directive that does not already exist). I've figured out how to hack around it, but the hack requires GNU make. We already use GNU make constructs elsewhere (such as $(wildcard)), but

It is just a wrapper around select(2). Signed-off-by: Wei Liu <wei.liu2@citrix.com> --- extras/mini-os/include/posix/poll.h | 1 + extras/mini-os/lib/sys.c | 90 ++++++++++++++++++++++++++++++++++- 2 files changed, 90 insertions(+), 1 deletion(-) create mode 100644 extras/mini-os/include/posix/poll.h diff --git a/extras/mini-os/include/posix/poll.h

Since Eric's improvements to the command queue in commit 6af72b8 (and following) there's now a queue of commands waiting to be issued stored in the handle, and there's no need to issue commands only from the ready state. We can therefore remove the want_to_send logic, queue as many commands as possible, and don't need to test if the socket is ready for POLLOUT. This commit also

The original implementation utilies select(). In Linux select() typically supports up to 1024 file descriptors. This can be a problem when user tries to boot up many guests. Switching to poll() has minimum impact on existing code and has better scalibility. Up to 8192 file descriptors are supported in the current implementation. Signed-off-by: Wei Liu <wei.liu2@citrix.com> ---

Since v2: - rebase to Rich's new API calls - more refactoring in patch 1 (retitled) - new patches 3 and 4 - fix data corruption in patch 6 (was 4) - more tweaks to the reproducer example (including using new API from 3) Eric Blake (7): lib: Refactor command_common() to do more common work commands: Allow for a command queue commands: Expose FIFO ordering of server completions

Let's check for a quite a few more errors. Among other things, this adds some coverage for a few things I've patched recently. --- And these enhancements set me up for my next fix: making NBD_CMD_DISC prevent future commands. tests/errors.c | 167 +++++++++++++++++++++++++++++++++++++++++++++---- 1 file changed, 154 insertions(+), 13 deletions(-) diff --git a/tests/errors.c

Mention things to remember for avoiding the deadlock of polling for a POLLIN from a server that has no replies to send. Perhaps we could split the READY state into two - one for when there are no commands in flight (and get_direction returns 0 to state that polling is pointless, although a multi-threaded reader can still poll for POLLIN), and the other when there ARE commands in flight. Such a

It is necessary to kick the state machine any time another thread blocks due to write() encountering a full buffer, to get the reader thread to learn that it must now poll on POLLOUT rather than just POLLIN. POSIX only provides two ways to do this: either poll() on a second fd (our pipe-to-self trick), or interrupt the polling with EINTR due to delivery of a signal. So, I played with the latter

--- This is what I used to provoke the deadlocks; before my patch series, it was succeeding for a fully-parallel server: nbdkit -U - memory 2M --run './deadlock $unixsocket' as well as for a serialized server that didn't trip up Linux kernel buffering limits: nbdkit -U - --filter=noparallel memory 256k --run './deadlock $unixsocket' but was reliably hanging with both client

Added merely as an example to be run by hand, rather than automated into 'make check', since nbdkit --filter=noparallel is quite new. --- .gitignore | 1 + examples/Makefile.am | 10 ++ examples/batched-read-write.c | 214 ++++++++++++++++++++++++++++++++++ 3 files changed, 225 insertions(+) create mode 100644 examples/batched-read-write.c diff --git

--- .gitignore | 1 + examples/Makefile.am | 12 + examples/concurrent-writer.c | 450 +++++++++++++++++++++++++++ examples/threaded-reads-and-writes.c | 2 +- 4 files changed, 464 insertions(+), 1 deletion(-) diff --git a/.gitignore b/.gitignore index 30438c1..e4dad91 100644 --- a/.gitignore +++ b/.gitignore @@ -41,6 +41,7 @@ Makefile.in