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[Qemu-devel] [PULL 36/42] spapr: Implement better workaround in spapr-vt
From: |
David Gibson |
Subject: |
[Qemu-devel] [PULL 36/42] spapr: Implement better workaround in spapr-vty device |
Date: |
Wed, 21 Aug 2019 17:25:36 +1000 |
From: Paul Mackerras <address@hidden>
Linux guest kernels have code which scans the string of characters
returned from the H_GET_TERM_CHAR hypercall and removes any \0
character which comes immediately after a \r character. This is to
work around a bug which was present in some ancient versions of
PowerVM. In order to avoid the corruption of the console byte stream
that this introduced, commit 6c3bc244d3cb ("spapr: Implement bug in
spapr-vty device to be compatible with PowerVM") added a workaround
which adds a \0 character after every \r character. Unfortunately,
this corrupts the console byte stream for those operating systems,
such as AIX, which don't remove the null bytes.
We can avoid triggering the Linux kernel workaround if we avoid
returning a buffer which contains a \0 after a \r. We can do that by
breaking out of the loop in vty_getchars() if we are about to insert a
\0 and the previous character in the buffer is a \r. That means we
return the characters up to the \r for the current H_GET_TERM_CHAR,
and the characters starting with the \0 for the next one.
With this workaround, we don't insert any spurious characters and we
avoid triggering the Linux kernel workaround, so the guest will
receive an uncorrupted stream whether or not they have the workaround.
Fixes: 6c3bc244d3cb ("spapr: Implement bug in spapr-vty device to be compatible
with PowerVM")
Signed-off-by: Paul Mackerras <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: David Gibson <address@hidden>
---
hw/char/spapr_vty.c | 30 ++++++++++++------------------
1 file changed, 12 insertions(+), 18 deletions(-)
diff --git a/hw/char/spapr_vty.c b/hw/char/spapr_vty.c
index 7f860fcce7..087c93e4fa 100644
--- a/hw/char/spapr_vty.c
+++ b/hw/char/spapr_vty.c
@@ -59,25 +59,19 @@ static int vty_getchars(SpaprVioDevice *sdev, uint8_t *buf,
int max)
int n = 0;
while ((n < max) && (dev->out != dev->in)) {
- buf[n++] = dev->buf[dev->out++ % VTERM_BUFSIZE];
-
- /* PowerVM's vty implementation has a bug where it inserts a
- * \0 after every \r going to the guest. Existing guests have
- * a workaround for this which removes every \0 immediately
- * following a \r, so here we make ourselves bug-for-bug
- * compatible, so that the guest won't drop a real \0-after-\r
- * that happens to occur in a binary stream. */
- if (buf[n - 1] == '\r') {
- if (n < max) {
- buf[n++] = '\0';
- } else {
- /* No room for the extra \0, roll back and try again
- * next time */
- dev->out--;
- n--;
- break;
- }
+ /*
+ * Long ago, PowerVM's vty implementation had a bug where it
+ * inserted a \0 after every \r going to the guest. Existing
+ * guests have a workaround for this which removes every \0
+ * immediately following a \r. To avoid triggering this
+ * workaround, we stop before inserting a \0 if the preceding
+ * character in the output buffer is a \r.
+ */
+ if (n > 0 && (buf[n - 1] == '\r') &&
+ (dev->buf[dev->out % VTERM_BUFSIZE] == '\0')) {
+ break;
}
+ buf[n++] = dev->buf[dev->out++ % VTERM_BUFSIZE];
}
qemu_chr_fe_accept_input(&dev->chardev);
--
2.21.0
- [Qemu-devel] [PULL 17/42] spapr: Implement H_CONFER, (continued)
- [Qemu-devel] [PULL 17/42] spapr: Implement H_CONFER, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 20/42] spapr: initial implementation for H_TPM_COMM/spapr-tpm-proxy, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 29/42] machine: Add wakeup method to MachineClass, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 23/42] ppc/xive: Implement TM_PULL_OS_CTX special command, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 34/42] spapr/pci: Free MSIs during reset, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 21/42] pseries: Update SLOF firmware image, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 37/42] spapr/xive: Mask the EAS when allocating an IRQ, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 25/42] ppc/xive: Provide escalation support, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 35/42] spapr/irq: Drop spapr_irq_msi_reset(), David Gibson, 2019/08/21
- [Qemu-devel] [PULL 28/42] ppc/xive: Improve 'info pic' support, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 36/42] spapr: Implement better workaround in spapr-vty device,
David Gibson <=
- [Qemu-devel] [PULL 38/42] target/ppc: Add Directed Privileged Door-bell Exception State (DPDES) SPR, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 30/42] i386: use machine class ->wakeup method, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 22/42] ppc/xive: use an abstract type for XiveNotifier, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 27/42] ppc/xive: Provide silent escalation support, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 41/42] ppc: Fix emulated INFINITY and NAN conversions, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 31/42] spapr: Implement ibm,suspend-me, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 24/42] ppc/xive: Provide backlog support, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 32/42] ppc: remove idle_timer logic, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 42/42] ppc: Fix emulated single to double denormalized conversions, David Gibson, 2019/08/21
- [Qemu-devel] [PULL 40/42] ppc: conform to processor User's Manual for xscvdpspn, David Gibson, 2019/08/21