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90e4d681bc
virFileOpenAs previously would only try opening a file as the current user, or as a different user, but wouldn't try both methods in a single call. This made it cumbersome to use as a replacement for open(2). Additionally, it had a lot of historical baggage that led to it being difficult to understand. This patch refactors virFileOpenAs in the following ways: * reorganize the code so that everything dealing with both the parent and child sides of the "fork+setuid+setgid+open" method are in a separate function. This makes the public function easier to understand. * Allow a single call to virFileOpenAs() to first attempt the open as the current user, and if that fails to automatically re-try after doing fork+setuid (if deemed appropriate, i.e. errno indicates it would now be successful, and the file is on a networkFS). This makes it possible (in many, but possibly not all, cases) to drop-in virFileOpenAs() as a replacement for open(2). (NB: currently qemuOpenFile() calls virFileOpenAs() twice, once without forking, then again with forking. That unfortunately can't be changed without at least some discussion of the ramifications, because the requested file permissions are different in each case, which is something that a single call to virFileOpenAs() can't deal with.) * Add a flag so that any fchown() of the file to a different uid:gid is explicitly requested when the function is called, rather than it being implied by the presence of the O_CREAT flag. This just makes for less subtle surprises to consumers. (Commit b1643dc15c5de886fefe56ad18608d65f1325a2c added the check for O_CREAT before forcing ownership. This patch just makes that restriction more explicit.) * If either the uid or gid is specified as "-1", virFileOpenAs will interpret this to mean "the current [gu]id". All current consumers of virFileOpenAs should retain their present behavior (after a few minor changes to their setup code and arguments).
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>