Re: [Libguestfs] [PATCH v2 0/3] library: improve handling of external tools
On Thu, Feb 02, 2017 at 02:33:17PM +0100, Pino Toscano wrote:
Hi,
the libguestfs library uses a number of external tools; for some of
them, we search for them at build time, enabling some feature only if
found, and later on assuming at runtime they are installed. However,
the situation is more complex than that:
- hardcoding the full path means that there is an incoherency in the
way some of the tools are used, as some other tools (e.g. qemu-img)
are just run as assumed to be in $PATH; also hardcoding means
libguestfs cannot use different versions of those tools
There is reasoning here, see m4/guestfs_programs.m4:
# Check for external programs required to either build or run
# libguestfs.
#
# AC_CHECK_PROG(S) or AC_PATH_PROG(S)?
#
# Use AC_CHECK_PROG(S) for programs which are only used during build.
#
# Use AC_PATH_PROG(S) for program names which are compiled into the
# binary and used at run time. The reason is so that we know which
# programs the binary actually uses.
As it says in the message, the main reason I like to hard code the
full path is because I want to know that the user is running the same
program that we tested against, ie. they didn't install some
half-baked binary in /usr/local/bin.
I think it's a mistake if we call qemu-img without the full path BTW ...
- some of the tools are actually optional, and their runtime lack
can
be handled gracefully instead of throwing a "failed to execute" error
Now, I do think this is a problem. But why don't we just test if the
(full pathnamed) program exists using a simple stat or access?
Rich.
The chosen approach is to build a process-wide cache in the
libguestfs
library of paths of tools searched, even in case they are not available:
this way it is easier to just skip something at runtime if a program is
not there. The patch series applies it for the libdb tools, and for
the tools used to extract icons from guests.
Thanks,
Pino Toscano (3):
lib: add internal cache for external application
lib: improve libdb tools handling at runtime (RHBZ#1409024)
inspect: make netpbm and icoutils really optional runtime tools
lib/Makefile.am | 1 +
lib/external-apps.c | 190 +++++++++++++++++++++++++++++++++++++++++++++
lib/guestfs-internal.h | 3 +
lib/inspect-apps.c | 14 +++-
lib/inspect-icon.c | 54 +++++++------
m4/guestfs-find-db-tool.m4 | 2 +-
m4/guestfs_progs.m4 | 24 ------
7 files changed, 237 insertions(+), 51 deletions(-)
create mode 100644 lib/external-apps.c
--
2.9.3
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