[PATCH 1/5] virfile: Introduce virCloseRange()

[Ján Tomko]

On a Tuesday in 2023, Michal Privoznik wrote:
>Linux gained new close_range() syscall (in v5.9) that allows
>closing a range of FDs in a single syscall. Ideally, we would use
>it to close FDs when spawning a process (e.g. via virCommand
>module).
>
>Glibc has close_range() wrapper over the syscall, which falls
>back to iterative closing of all FDs inside the range if running
>under older kernel. We don't wan that as in that case we might

want

>just close opened FDs (see Linux version of
>virCommandMassClose()). And musl doesn't have close_range() at
>all. Therefore, call syscall directly.
>
>Now, mass close of FDs happen in a fork()-ed off child. While it

happens

>could detect whether the kernel does support close_range(), it
>has no way of passing this info back to the parent and thus each
>child would need to query it again and again.
>
>Since this can't change while we are running we can cache the
>information - hence virCloseRangeInit().
>
>Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
>---
> src/libvirt_private.syms |  3 ++
> src/util/virfile.c       | 89 ++++++++++++++++++++++++++++++++++++++++
> src/util/virfile.h       |  4 ++
> 3 files changed, 96 insertions(+)
>
>diff --git a/src/util/virfile.c b/src/util/virfile.c
>index fe456596ae..7696910e00 100644
>--- a/src/util/virfile.c
>+++ b/src/util/virfile.c
>+static void
>+virCloseRangeOnceInit(void)
>+{
>+    int fd[2] = { -1, -1};

Uneven spacing.

>+
>+    if (virPipeQuiet(fd) < 0)
>+        return;
>+
>+    VIR_FORCE_CLOSE(fd[1]);
>+    if (virCloseRangeImpl(fd[0], fd[0]) < 0) {
>+        VIR_FORCE_CLOSE(fd[0]);
>+        return;
>+    }
>+
>+    virCloseRangeSupported = true;
>+}
>+
>+

Reviewed-by: Ján Tomko <jtomko at redhat.com>

Jano
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