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qapi/parser: Don't try to handle file errors
John Snow authored 
Fixes: f5d4361c
Fixes: 52a47418
Fixes: 46f49468

Remove the try/except block that handles file-opening errors in
QAPISchemaParser.__init__() and add one each to
QAPISchemaParser._include() and QAPISchema.__init__() respectively.

This simultaneously fixes the typing of info.fname (f5d4361c), A
static typing violation in test-qapi (46f49468), and a regression of
an error message (52a47418).

The short-ish version of what motivates this patch is:

- It's hard to write a good error message in the init method,
  because we need to determine the context of our caller to do so.
  It's easier to just let the caller write the message.
- We don't want to allow QAPISourceInfo(None, None, None) to exist. The
  typing introduced by commit f5d4361c types the 'fname' field as
  (non-optional) str, which was premature until the removal of this
  construct.
- Errors made using such an object are currently incorrect (since
  52a47418)
- It's not technically a semantic error if we cannot open the schema.
- There are various typing constraints that make mixing these two cases
  undesirable for a single special case.
- test-qapi's code handling an fname of 'None' is now dead, drop it.
  Additionally, Not all QAPIError objects have an 'info' field (since
  46f49468), so deleting this stanza corrects a typing oversight in
  test-qapi introduced by that commit.

Other considerations:

- open() is moved to a 'with' block to ensure file pointers are
  cleaned up deterministically.
- Python 3.3 deprecated IOError and made it a synonym for OSError.
  Avoid the misleading perception these exception handlers are
  narrower than they really are.

The long version:

The error message here is incorrect (since commit 52a47418):

> python3 qapi-gen.py 'fake.json'
qapi-gen.py: qapi-gen.py: can't read schema file 'fake.json': No such file or directory

In pursuing it, we find that QAPISourceInfo has a special accommodation
for when there's no filename. Meanwhile, the intent when QAPISourceInfo
was typed (f5d4361c) was non-optional 'str'. This usage was
overlooked.

To remove this, I'd want to avoid having a "fake" QAPISourceInfo
object. I also don't want to explicitly begin accommodating
QAPISourceInfo itself being None, because we actually want to eventually
prove that this can never happen -- We don't want to confuse "The file
isn't open yet" with "This error stems from a definition that wasn't
defined in any file".

(An earlier series tried to create a dummy info object, but it was tough
to prove in review that it worked correctly without creating new
regressions. This patch avoids that distraction. We would like to first
prove that we never raise QAPISemError for any built-in object before we
add "special" info objects. We aren't ready to do that yet.)

So, which way out of the labyrinth?

Here's one way: Don't try to handle errors at a level with "mixed"
semantic contexts; i.e. don't mix inclusion errors (should report a
source line where the include was triggered) and command line errors
(where we specified a file we couldn't read).

Remove the error handling from the initializer of the parser. Pythonic!
Now it's the caller's job to figure out what to do about it. Handle the
error in QAPISchemaParser._include() instead, where we can write a
targeted error message where we are guaranteed to have an 'info' context
to report with.

The root level error can similarly move to QAPISchema.__init__(), where
we know we'll never have an info context to report with, so we use a
more abstract error type.

Now the error looks sensible again:

> python3 qapi-gen.py 'fake.json'
qapi-gen.py: can't read schema file 'fake.json': No such file or directory

With these error cases separated, QAPISourceInfo can be solidified as
never having placeholder arguments that violate our desired types. Clean
up test-qapi along similar lines.

Signed-off-by: default avatarJohn Snow <jsnow@redhat.com>
Message-Id: <20210519183951.3946870-2-jsnow@redhat.com>
Reviewed-by: default avatarMarkus Armbruster <armbru@redhat.com>
Signed-off-by: default avatarMarkus Armbruster <armbru@redhat.com>
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block.c
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blockjob.c
configure
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cpus-common.c
disas.c
gdbstub.c
gitdm.config
hmp-commands-info.hx
hmp-commands.hx
iothread.c
job-qmp.c
job.c
memory_ldst.c.inc
meson.build
meson_options.txt
module-common.c
os-posix.c
os-win32.c
page-vary-common.c
page-vary.c
qemu-bridge-helper.c
qemu-edid.c
README.rst

QEMU README

QEMU is a generic and open source machine & userspace emulator and virtualizer.

QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board).

QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation.

QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager.

QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file.

Documentation

Documentation can be found hosted online at https://www.qemu.org/documentation/. The documentation for the current development version that is available at https://www.qemu.org/docs/master/ is generated from the docs/ folder in the source tree, and is built by Sphinx <https://www.sphinx-doc.org/en/master/>_.

Building

QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are:

mkdir build
cd build
../configure
make

Additional information can also be found online via the QEMU website:

Submitting patches

The QEMU source code is maintained under the GIT version control system.

git clone https://gitlab.com/qemu-project/qemu.git

When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the style section <https://www.qemu.org/docs/master/devel/style.html> of the Developers Guide.

Additional information on submitting patches can be found online via the QEMU website

The QEMU website is also maintained under source control.

git clone https://gitlab.com/qemu-project/qemu-web.git

A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once.

For installation instructions, please go to

The workflow with 'git-publish' is:

$ git checkout master -b my-feature
$ # work on new commits, add your 'Signed-off-by' lines to each
$ git publish

Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future.

Sending v2:

$ git checkout my-feature # same topic branch
$ # making changes to the commits (using 'git rebase', for example)
$ git publish

Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2.

Bug reporting

The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs found when running code built from QEMU git or upstream released sources should be reported via:

If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via launchpad.

For additional information on bug reporting consult:

ChangeLog

For version history and release notes, please visit https://wiki.qemu.org/ChangeLog/ or look at the git history for more detailed information.

Contact

The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC

Information on additional methods of contacting the community can be found online via the QEMU website: