On 13.09.2016 02:21, Julio Faracco wrote:
> Libvirtd only support hooks when the daemon is started. Hooks cannot be
> loaded when the daemon is already running. So, to load a hook you need to
> restart the service everytime. Now, the inotify support enables the option
> of create a hook and run it even if libvirtd was started.
>
> Cc: Carlos Castilho <ccasti@xxxxxxxxxx>
> Signed-off-by: Julio Faracco <jcfaracco@xxxxxxxxx>
Interesting approach. The only thing I am worried about is that it might
trick users into thinking we will implement something similar for
editing XML files for domains. That is, if they edit
/etc/libvirt/qemu/myFavouriteDomain.xml, libvirt will monitor the
changes and re-read the file if needed.
> ---
> daemon/libvirtd.c | 1 +
> src/libvirt_private.syms | 1 +
> src/util/virhook.c | 165 ++++++++++++++++++++++++++++++++++++++++++++++-
> src/util/virhook.h | 10 +++
> 4 files changed, 175 insertions(+), 2 deletions(-)
The documentation is missing. There is docs/hooks.html.in file which
covers this topic.
Moreover, 'make all syntax-check check' is your friend ;-)
I'm not gonna report problems found by syntax-check - now that you know
we have such feature, you can fix those issues yourself.
>
> diff --git a/daemon/libvirtd.c b/daemon/libvirtd.c
> index 95c1b1c..56175d1 100644
> --- a/daemon/libvirtd.c
> +++ b/daemon/libvirtd.c
> @@ -1622,6 +1622,7 @@ int main(int argc, char **argv) {
> 0, "shutdown", NULL, NULL);
>
> cleanup:
> + virHookCleanUp();
> virNetlinkEventServiceStopAll();
> virObjectUnref(remoteProgram);
> virObjectUnref(lxcProgram);
> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
> index 6a77e46..c8ad816 100644
> --- a/src/libvirt_private.syms
> +++ b/src/libvirt_private.syms
> @@ -1648,6 +1648,7 @@ virHashValueFree;
> virHookCall;
> virHookInitialize;
> virHookPresent;
> +virHookCleanUp;
>
>
> # util/virhostdev.h
> diff --git a/src/util/virhook.c b/src/util/virhook.c
> index facd74a..d5fc928 100644
> --- a/src/util/virhook.c
> +++ b/src/util/virhook.c
> @@ -26,6 +26,7 @@
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <sys/stat.h>
> +#include <sys/inotify.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
> @@ -45,6 +46,10 @@ VIR_LOG_INIT("util.hook");
>
> #define LIBVIRT_HOOK_DIR SYSCONFDIR "/libvirt/hooks"
>
> +#define virHookInstall(driver) virHooksFound |= (1 << driver);
> +
> +#define virHookUninstall(driver) virHooksFound ^= (1 << driver);
> +
> VIR_ENUM_DECL(virHookDriver)
> VIR_ENUM_DECL(virHookDaemonOp)
> VIR_ENUM_DECL(virHookSubop)
> @@ -109,6 +114,8 @@ VIR_ENUM_IMPL(virHookLibxlOp, VIR_HOOK_LIBXL_OP_LAST,
>
> static int virHooksFound = -1;
>
> +static virHookInotifyPtr virHooksInotify = NULL;
> +
> /**
> * virHookCheck:
> * @driver: the driver name "daemon", "qemu", "lxc"...
> @@ -153,6 +160,121 @@ virHookCheck(int no, const char *driver)
> return ret;
> }
>
> +/**
> + * virHookInotifyEvent:
> + * @fd: inotify file descriptor.
> + *
> + * Identifies file events at libvirt's hook directory.
> + * Install or uninstall hooks on demand. Acording file manipulation.
> + */
> +static void
> +virHookInotifyEvent(int watch ATTRIBUTE_UNUSED,
> + int fd,
> + int events ATTRIBUTE_UNUSED,
> + void *data ATTRIBUTE_UNUSED)
> +{
> + char buf[1024];
man page suggests using slightly larger buffer.
> + struct inotify_event *e;
> + int got;
> + int driver;
> + char *tmp, *name;
> +
> + VIR_DEBUG("inotify event in virHookInotify()");
> +
> +reread:
> + got = read(fd, buf, sizeof(buf));
@fd is blocking. We don't want to read from a blocking FD in our event
loop (as it might block the whole event loop).
> + if (got == -1) {
> + if (errno == EINTR)
> + goto reread;
> + return;
> + }
We have a wrapper for that - saferead(). Also, it would be nice if an
error is reported on failed read. Just imagine you're given the daemon
logs with bug description 'libvirt hooks do not work with inotify'.
> +
> + tmp = buf;
> + while (got) {
> + if (got < sizeof(struct inotify_event))
> + return;
> +
> + VIR_WARNINGS_NO_CAST_ALIGN
> + e = (struct inotify_event *)tmp;
> + VIR_WARNINGS_RESET
> +
> + tmp += sizeof(struct inotify_event);
> + got -= sizeof(struct inotify_event);
> +
> + if (got < e->len)
> + return;
Wait, what? This discards partially read event. Moreover, in the next
iteration we start reading from wrong offset in the inotify_event struct
and thus poison the well. I think we need to come up with better
mechanism for reading events. Also - should we allocate receiving buffer
for events dynamically on demand?
> +
> + tmp += e->len;
> + got -= e->len;
> +
> + name = (char *)&(e->name);
This does not feel right. e->name is type of ' char[]'.
> +
> + /* Removing hook file. */
> + if (e->mask & (IN_DELETE | IN_MOVED_FROM)) {
> + if ((driver = virHookDriverTypeFromString(name)) < 0) {
> + VIR_DEBUG("Invalid hook name for %s", name);
> + return;
> + }
> +
> + virHookUninstall(driver);
> + }
> +
> + /* Creating hook file. */
> + if (e->mask & (IN_CREATE | IN_CLOSE_WRITE | IN_MOVED_TO)) {
> + if ((driver = virHookDriverTypeFromString(name)) < 0) {
> + VIR_DEBUG("Invalid hook name for %s", name);
> + return;
> + }
> +
> + virHookInstall(driver);
> + }
> + }
> +}
Well, this just sets some internal variable. It doesn't reload the list
of hooks or something. Moreover, these hooks are meant to be run at the
daemon startup. Therefore I think you should stick to what I suggest in
the other e-mail.
Michal
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