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Revision as of 18:26, 19 June 2018 by ColeRobinson (talk | contribs) (Remove domain_conf, qemu_driver, virsh_edit tasks. Nice ideas but really aren't good fits for beginners and may be controversial)
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This page tracks introductory tasks for new libvirt contributors. Code cleanups, bugs, and small features are listed with difficulty ranging from trivial to intermediate.

Introductory bug reports (LibvirtFirstBug)

Some bugs in the libvirt bugzilla tracker are marked as good introductory bug reports for new contributors. These bugs have the 'LibvirtFirstBug' tag. Each bug report contains info and sample commits to point you in the right direction. You can open the list in your browser bugzilla here.

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Many VIR_ERROR()/VIR_WARN() usages should show virGetLastErrorMessage()

There's many places in the code that call VIR_ERROR and VIR_WARN after a function fails, but they don't report the error message raised by the failing function. virGetLastErrorMessage() will give us the string error from the failing function, so we can use that. Some examples that should be updated:

  • Every VIR_WARN in src/qemu/qemu_capabilities.c function virQEMUCapsInit
  • Nearly every VIR_WARN and VIR_ERROR in src/qemu/qemu_process.c
  • Every VIR_WARN in src/lxc/lxc_driver.c

Example patch:

qemu: Use comma escaping for more command line values

Most qemu command line arguments take the form of -OPTION ARG1=VALUE1,ARG2=VALUE2,... This format presents a problem when one of the values we want to pass has a comma ',' in it. qemu handles this by requiring callers to escape a comma... with another comma! So if we want to pass /path-with-,.foo to qemu, it must be turned into /path-with-,,.foo. We already handle several items like this in libvirt but there's many more that need comma escaping, and there's a convenience function for it called virQEMUBuildBufferEscapeComma.

Example patches that adds some comma escaping: More here: More here:

Here's some examples, find their usages in src/qemu/qemu_command.c and add virQEMUBuildBufferEscapeComma calls used in the above patches.

  • Building the source drive string in qemuBuildNetworkDriveURI, qemuBuildNetworkDriveStr, and qemuGetDriveSourceString (src->hosts->socket, NBD exportname=src->path, Sheepdog src->path processing, rbd src->path & configFile processing,
  • Validate whether TYPE_FILE needs to follow TYPE_DEV and TYPE_PIPE handling in qemuBuildChrChardevStr
  • socket.address processing in qemuBuildHostNetStr (localaddr for UDP too)_
  • group_name processing in qemuBuildDiskThrottling

Add *DefNew and functions for all device objects

Not all device objects have associated *DefNew functions. For example, in src/conf/domain_conf.c virDomainDiskDefPtr has a virDomainDiskDefNew, but virDomainSmartcardDefPtr doesn't have a similar virDomainSmartcardDefNew. Not all devices strictly require it, but adding it ahead of time simplifies cases in the future when it might be needed.

As an example, see this commit which added virDomainVideoDefNew:

Move virDomainVideoDefaultType logic to individual drivers

The virDomainVideoDefaultType function in src/conf/domain_conf.c shouldn't be there :) The logic setting a device default should be in the post parse function of individual driver code.

See this example commit that moves logic out of that function and into the qemu driver:

Code Cleanups

Remove virDomainDefNewFull()

The function virDomainDefNewFull() in src/conf/domain_conf.c is a thin wrapper around virDomainDefNew() that is only used in a few places in the code. It should be removed, and the function callers just re-implement the minimal functionality it provides.

Split apart virDomainObjAssignDef()

The virDomainObjAssignDef() function takes 4 arguments, the latter 2 'live' and 'oldDef' are very rarely used. The function should be reworked to provide 3 functions instead:

  • Rename virDomainObjAssignDef() to virDomainObjAssignDefGetOldDef()
  • Add virDomainObjAssignDefLive(arg1, arg2) which does virDomainObjAssignDefGetOldDef(arg1, arg2, true, NULL);
  • Add virDomainObjAssignDef(arg1, arg2) which does virDomainObjAssignDefGetOldDef(arg1, arg2, false, NULL);

All the callers will need to be adjusted, but it will be much more clear what those callers actually do.

Move validation checks out of domain XML parsing

The code that handles domain/VM XML parsing (virDomainDefParseXML in src/domain/domain_conf.c) has various validation checks sprinkled within it. Many of these checks should be moved out of the parse step and into virDomainDefPostParse, so they can be shared by various places in the code that build a domain definition without XML, such as converting from native vmware/virtualbox/xen formats.

Not all validation checks can or should be moved. You'll need to determine if the check is specific to the actual XML parsing, or is it general for all VM configurations. So anything that throws an error if it hits unexpected XML should not be moved.

Just a few of the candidates for moving to virDomainDefPostParse:

  • All the errors in virDomainDefParseXML containing the string "usb is disabled"
  • All the errors in virDomainDefParseXML containing the string "period must be in range"
  • All the errors in virDomainDefParseXML containing the string "quota must be in range"
  • The error "tray is only valid for cdrom and floppy"
  • The error "removable is only valid for usb disks"
  • Many other checks in virDomainDiskDefParseXML

Share cgroup code that is duplicated between QEMU and LXC

INTERMEDIATE: Both QEMU and LXC drivers have some similar code when dealing with cgroups. See various routines in src/lxc/lxc_cgroup.c and src/qemu/qemu_cgroup.c, there is lots of opportunity for centralizing functionality in src/util/vircgroup.c. For example:

  • virLXCCgroupSetupBlkioTune() and qemuSetupBlkioCgroup() are similar
  • virLXCCgroupSetupCpuTune() and qemuSetupCpuCgroup() are similar

Share duplicated daemon code

INTERMEDIATE: Libvirt ships several daemons (libvirtd, virtlogd, virtlockd) that all have similar code around general daemon startup. Right now the code is duplicated for each daemon, but it could be shared, like in a new file src/util/virdaemon.c. The main files to look in are src/logging/log_daemon.c, src/locking/lock_daemon.c, and daemon/libvirtd.c. Some example functions to look at:

  • the *ForkIntoBackground functions
  • the *SetupLogging functions
  • the *SetupSignals functions
  • the *DaemonClientNew functions
  • the *UnicSocketPaths functions

Clean up virQEMUDriverPtr parameters

EXTREMELY BEGINNER: Many functions in the QEMU driver code (src/qemu/) take both a domain object and a driver as a parameter. However, since 2e6ecba1bcac, a pointer to the driver structure is saved in private data of the domain object. That can be used instead of a parameter being passed to various functions (a git grep for 'virQEMUDriverPtr driver,' shows some applicable candidates).

Example patch:

Clean up virBufferCheckError() callers

BEGINNER: There is a concept of dynamically allocated buffer in libvirt, called virBuffer. One of its advantages is that functions working with this buffer do not report error or have any return value. The error is stored in the structure itself. While long-winded manipulations with virBuffer are easy and clean thanks to this (no need to check for error after every single append of data), the disadvantage is that every time the data is received from the buffer there needs to be check for the possibility of an error and the data received. These two things are not always needed both or done together, however in most places it is. While this handling needed a condition and a check, it is now a little bit easier to do this and older code should be cleaned up to use the new approach.

Example patch:

More conversions to virErrorPreserveLast/virErrorRestore

virErrorPreserveLast + virErrorRestore are newer internal APIs for saving and restoring error reports. 'git grep virSaveLastError' and most usages will be candidates for converting.

See this commit for example conversions in qemu_hotplug.c:

Clean up variables in tools/

BEGINNER: The script has many functions that just redeclare variables all over the place instead of making them local to the function using the `local` keyword. There might be some errors due to the rewriting of the variables and it's also prone to error, so all such variables should be marked `local`. There is at least one function that returns an information in a variable. Such occurrences might be fixed up or kept that way.

Change testutils.[ch] referencing in tests/

BEGINNER: Go through the rules in the file and see how can the files `testutils.[ch]` be referenced so that the rules are smaller. There are various ways how to do that and it is left as an exercise to the implementer to figure out which one is the best. And to possibly discuss that on the list.

Ideas include:

  • Create object file of testutils and add that to each tests' testname_LDADD
  • Add it to LDADD in that file so that it's included in all the tests
  • Create a variable TESTUTILS and use that instead of testutils.[ch]
  • etc.

Remove redundant uses of *.la in Makefiles

BEGINNER: There is variable LDADDS in most of the Makefiles that is used for most of the targets in the Makefile. So specifying it separately just pollutes the file for no benefit. Check for such cases, fix them and think of a way automatically checking whether that happens.