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  1. 02 2月, 2018 6 次提交
    • G
      tests: virtio-9p: add LOPEN operation test · 82469aae
      由 Greg Kurz 提交于 
      Trivial test of a successful open.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
      82469aae
    • G
      tests: virtio-9p: use the synth backend · 2893ddd5
      由 Greg Kurz 提交于 
      The purpose of virtio-9p-test is to test the virtio-9p device, especially
the 9p server state machine. We don't really care what fsdev backend we're
using. Moreover, if we want to be able to test the flush request or a
device reset with in-flights I/O, it is close to impossible to achieve
with a physical backend because we cannot ask it reliably to put an I/O
on hold at a specific point in time.

Fortunately, we can do that with the synthetic backend, which allows to
register callbacks on read/write accesses to a specific file. This will
be used by a later patch to test the 9P flush request.

The walk request test is converted to using the synth backend.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
      2893ddd5
    • G
      tests: virtio-9p: wait for completion in the test code · 60b1fa9d
      由 Greg Kurz 提交于 
      In order to test request cancellation, we will need to send multiple
requests and wait for the associated replies. Since we poll the ISR
to know if a request completed, we may have several replies to parse
when we detect ISR was set to 1.

This patch moves the waiting out of the reply parsing path, up into
the functional tests.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
      60b1fa9d
    • G
      tests: virtio-9p: move request tag to the test functions · 693b21d2
      由 Greg Kurz 提交于 
      It doesn't really makes sense to hide the request tag from the test
functions. It prevents to test the 9p server behavior when passed
a wrong tag (ie, still in use or different from P9_NOTAG for a
version request). Also the spec says that a tag is reusable as soon
as the corresponding request was replied or flushed: no need to
always increment tags like we do now. And finaly, an upcoming test
of the flush command will need to manipulate tags explicitely.

This simply changes all request functions to have a tag argument.
Except for the version request which needs P9_NOTAG, all other
tests can pass 0 since they wait for the reply before sending
another request.
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
      693b21d2
    • K
      9pfs: Correctly handle cancelled requests · fc78d5ee
      由 Keno Fischer 提交于 
      # Background

I was investigating spurious non-deterministic EINTR returns from
various 9p file system operations in a Linux guest served from the
qemu 9p server.

 ## EINTR, ERESTARTSYS and the linux kernel

When a signal arrives that the Linux kernel needs to deliver to user-space
while a given thread is blocked (in the 9p case waiting for a reply to its
request in 9p_client_rpc -> wait_event_interruptible), it asks whatever
driver is currently running to abort its current operation (in the 9p case
causing the submission of a TFLUSH message) and return to user space.
In these situations, the error message reported is generally ERESTARTSYS.
If the userspace processes specified SA_RESTART, this means that the
system call will get restarted upon completion of the signal handler
delivery (assuming the signal handler doesn't modify the process state
in complicated ways not relevant here). If SA_RESTART is not specified,
ERESTARTSYS gets translated to EINTR and user space is expected to handle
the restart itself.

 ## The 9p TFLUSH command

The 9p TFLUSH commands requests that the server abort an ongoing operation.
The man page [1] specifies:

```
If it recognizes oldtag as the tag of a pending transaction, it should
abort any pending response and discard that tag.
[...]
When the client sends a Tflush, it must wait to receive the corresponding
Rflush before reusing oldtag for subsequent messages. If a response to the
flushed request is received before the Rflush, the client must honor the
response as if it had not been flushed, since the completed request may
signify a state change in the server
```

In particular, this means that the server must not send a reply with the
orignal tag in response to the cancellation request, because the client is
obligated to interpret such a reply as a coincidental reply to the original
request.

 # The bug

When qemu receives a TFlush request, it sets the `cancelled` flag on the
relevant pdu. This flag is periodically checked, e.g. in
`v9fs_co_name_to_path`, and if set, the operation is aborted and the error
is set to EINTR. However, the server then violates the spec, by returning
to the client an Rerror response, rather than discarding the message
entirely. As a result, the client is required to assume that said Rerror
response is a result of the original request, not a result of the
cancellation and thus passes the EINTR error back to user space.
This is not the worst thing it could do, however as discussed above, the
correct error code would have been ERESTARTSYS, such that user space
programs with SA_RESTART set get correctly restarted upon completion of
the signal handler.
Instead, such programs get spurious EINTR results that they were not
expecting to handle.

It should be noted that there are plenty of user space programs that do not
set SA_RESTART and do not correctly handle EINTR either. However, that is
then a userspace bug. It should also be noted that this bug has been
mitigated by a recent commit to the Linux kernel [2], which essentially
prevents the kernel from sending Tflush requests unless the process is about
to die (in which case the process likely doesn't care about the response).
Nevertheless, for older kernels and to comply with the spec, I believe this
change is beneficial.

 # Implementation

The fix is fairly simple, just skipping notification of a reply if
the pdu was previously cancelled. We do however, also notify the transport
layer that we're doing this, so it can clean up any resources it may be
holding. I also added a new trace event to distinguish
operations that caused an error reply from those that were cancelled.

One complication is that we only omit sending the message on EINTR errors in
order to avoid confusing the rest of the code (which may assume that a
client knows about a fid if it sucessfully passed it off to pud_complete
without checking for cancellation status). This does mean that if the server
acts upon the cancellation flag, it always needs to set err to EINTR. I
believe this is true of the current code.

[1] https://9fans.github.io/plan9port/man/man9/flush.html
[2] https://github.com/torvalds/linux/commit/9523feac272ccad2ad8186ba4fcc891Signed-off-by: NKeno Fischer <keno@juliacomputing.com>
Reviewed-by: NGreg Kurz <groug@kaod.org>
[groug, send a zero-sized reply instead of detaching the buffer]
Signed-off-by: NGreg Kurz <groug@kaod.org>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>
Reviewed-by: NStefano Stabellini <sstabellini@kernel.org>
      fc78d5ee
    • G
      9pfs: drop v9fs_register_transport() · 066eb006
      由 Greg Kurz 提交于 
      No good reasons to do this outside of v9fs_device_realize_common().
Signed-off-by: NGreg Kurz <groug@kaod.org>
Reviewed-by: NStefano Stabellini <sstabellini@kernel.org>
      066eb006
  3. 31 1月, 2018 34 次提交