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Libvirt provides a portable, long term stable C API for managing the
virtualization technologies provided by many operating systems. It
includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware
vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER
Hypervisor.
85b22f528f
I noticed when writing the backend functions for virNetworkUpdate that I was repeating the same sequence of memmove, VIR_REALLOC, nXXX-- (and messed up the args to memmove at least once), and had seen the same sequence in a lot of other places, so I decided to write a few utility functions/macros - see the .h file for full documentation. The intent is to reduce the number of lines of code, but more importantly to eliminate the need to check the element size and element count arithmetic every time we need to do this (I *always* make at least one mistake.) VIR_INSERT_ELEMENT: insert one element at an arbitrary index within an array of objects. The size of each object is determined automatically by the macro using sizeof(*array). The new element's contents are copied into the inserted space, then the original copy of contents are 0'ed out (if everything else was successful). Compile-time assignment and size compatibility between the array and the new element is guaranteed (see explanation below [*]) VIR_INSERT_ELEMENT_COPY: identical to VIR_INSERT_ELEMENT, except that the original contents of newelem are not cleared to 0 (i.e. a copy is made). VIR_APPEND_ELEMENT: This is just a special case of VIR_INSERT_ELEMENT that "inserts" one past the current last element. VIR_APPEND_ELEMENT_COPY: identical to VIR_APPEND_ELEMENT, except that the original contents of newelem are not cleared to 0 (i.e. a copy is made). VIR_DELETE_ELEMENT: delete one element at an arbitrary index within an array of objects. It's assumed that the element being deleted is already saved elsewhere (or cleared, if that's what is appropriate). All five of these macros have an _INPLACE variant, which skips the memory re-allocation of the array, assuming that the caller has already done it (when inserting) or will do it later (when deleting). Note that VIR_DELETE_ELEMENT* can return a failure, but only if an invalid index is given (index + amount to delete is > current array size), so in most cases you can safely ignore the return (that's why the helper function virDeleteElementsN isn't declared with ATTRIBUTE_RETURN_CHECK). A warning is logged if this ever happens, since it is surely a coding error. [*] One initial problem with the INSERT and APPEND macros was that, due to both the array pointer and newelem pointer being cast to void* when passing to virInsertElementsN(), any chance of type-checking was lost. If we were going to move in newelem with a memmove anyway, we would be no worse off for this. However, most current open-coded insert/append operations use direct struct assignment to move the new element into place (or just populate the new element directly) - thus use of the new macros would open a possibility for new usage errors that didn't exist before (e.g. accidentally sending &newelemptr rather than newelemptr - I actually did this quite a lot in my test conversions of existing code). But thanks to Eric Blake's clever thinking, I was able to modify the INSERT and APPEND macros so that they *do* check for both assignment and size compatibility of *ptr (an element in the array) and newelem (the element being copied into the new position of the array). This is done via clever use of the C89-guaranteed fact that the sizeof() operator must have *no* side effects (so an assignment inside sizeof() is checked for validity, but not actually evaluated), and the fact that virInsertElementsN has a "# of new elements" argument that we want to always be 1. |
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| build-aux | ||
| daemon | ||
| docs | ||
| examples | ||
| gnulib | ||
| include | ||
| m4 | ||
| po | ||
| python | ||
| src | ||
| tests | ||
| tools | ||
| .dir-locals.el | ||
| .gitignore | ||
| .gitmodules | ||
| .mailmap | ||
| AUTHORS.in | ||
| autobuild.sh | ||
| autogen.sh | ||
| bootstrap | ||
| bootstrap.conf | ||
| cfg.mk | ||
| ChangeLog-old | ||
| configure.ac | ||
| COPYING.LIB | ||
| HACKING | ||
| libvirt.pc.in | ||
| libvirt.spec.in | ||
| Makefile.am | ||
| Makefile.nonreentrant | ||
| mingw-libvirt.spec.in | ||
| README | ||
| README-hacking | ||
| run.in | ||
| TODO | ||
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>