Allow limiting the amount of log output sent. Allow up to 1 MiB.
In case the guest log buffer is larger than 1 MiB limit the output
instead of throwing an error.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
hw/uefi/ovmf-log.c | 40 ++++++++++++++++++++++++++++++++--------
hmp-commands-info.hx | 5 ++---
qapi/machine.json | 3 +++
3 files changed, 37 insertions(+), 11 deletions(-)
diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
index f03e47a290d6..9d9dc7b0d8d5 100644
--- a/hw/uefi/ovmf-log.c
+++ b/hw/uefi/ovmf-log.c
@@ -19,6 +19,7 @@
#include "qapi/error.h"
#include "qapi/type-helpers.h"
#include "qapi/qapi-commands-machine.h"
+#include "qobject/qdict.h"
/* ----------------------------------------------------------------------- */
@@ -167,7 +168,8 @@ static void handle_ovmf_log_range(GString *out,
}
}
-FirmwareLog *qmp_query_firmware_log(Error **errp)
+FirmwareLog *qmp_query_firmware_log(bool have_maxsize, uint64_t maxsize,
+ Error **errp)
{
MEM_DEBUG_LOG_HDR header;
dma_addr_t offset, base;
@@ -187,18 +189,38 @@ FirmwareLog *qmp_query_firmware_log(Error **errp)
return NULL;
}
- if (header.DebugLogSize > MiB) {
- /* default size is 128k (32 pages), allow up to 1M */
- error_setg(errp, "firmware log: log buffer is too big");
- return NULL;
- }
-
if (header.DebugLogHeadOffset > header.DebugLogSize ||
header.DebugLogTailOffset > header.DebugLogSize) {
error_setg(errp, "firmware log: invalid header");
return NULL;
}
+ if (!have_maxsize) {
+ maxsize = MiB;
+ }
+ if (maxsize > MiB) {
+ maxsize = MiB;
+ }
+
+ /* adjust header.DebugLogHeadOffset so we rezturn at most maxsize bytes */
+ if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
+ /* wrap around */
+ if (header.DebugLogTailOffset > maxsize) {
+ header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
+ } else {
+ uint64_t maxchunk = maxsize - header.DebugLogTailOffset;
+ if (header.DebugLogSize > maxchunk &&
+ header.DebugLogHeadOffset < header.DebugLogSize - maxchunk) {
+ header.DebugLogHeadOffset = header.DebugLogSize - maxchunk;
+ }
+ }
+ } else {
+ if (header.DebugLogTailOffset > maxsize &&
+ header.DebugLogHeadOffset < header.DebugLogTailOffset - maxsize) {
+ header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
+ }
+ }
+
base = offset + header.HeaderSize;
if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
/* wrap around */
@@ -237,8 +259,10 @@ void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
{
Error *errp = NULL;
FirmwareLog *log;
+ int64_t maxsize;
- log = qmp_query_firmware_log(&errp);
+ maxsize = qdict_get_try_int(qdict, "maxsize", -1);
+ log = qmp_query_firmware_log(maxsize != -1, (uint64_t)maxsize, &errp);
if (errp) {
hmp_handle_error(mon, errp);
return;
diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
index 257015f0b403..db03d88d3c74 100644
--- a/hmp-commands-info.hx
+++ b/hmp-commands-info.hx
@@ -980,11 +980,10 @@ ERST
{
.name = "firmware-log",
- .args_type = "",
- .params = "",
+ .args_type = "maxsize:i?",
+ .params = "[maxsize]",
.help = "show the firmware (ovmf) debug log",
.cmd = hmp_info_firmware_log,
- .flags = "p",
},
SRST
diff --git a/qapi/machine.json b/qapi/machine.json
index c96e582afdd6..d0c6d3ede027 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1857,9 +1857,12 @@
#
# Find firmware memory log buffer in guest memory, return content.
#
+# @maxsize: limit the amount of logdata returned.
+#
# Since: 10.2
##
{ 'command': 'query-firmware-log',
+ 'data': { '*maxsize': 'size' },
'returns': 'FirmwareLog' }
##
--
2.51.0Gerd Hoffmann <kraxel@redhat.com> writes:
> Allow limiting the amount of log output sent. Allow up to 1 MiB.
> In case the guest log buffer is larger than 1 MiB limit the output
> instead of throwing an error.
>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> hw/uefi/ovmf-log.c | 40 ++++++++++++++++++++++++++++++++--------
> hmp-commands-info.hx | 5 ++---
> qapi/machine.json | 3 +++
> 3 files changed, 37 insertions(+), 11 deletions(-)
>
> diff --git a/hw/uefi/ovmf-log.c b/hw/uefi/ovmf-log.c
> index f03e47a290d6..9d9dc7b0d8d5 100644
> --- a/hw/uefi/ovmf-log.c
> +++ b/hw/uefi/ovmf-log.c
> @@ -19,6 +19,7 @@
> #include "qapi/error.h"
> #include "qapi/type-helpers.h"
> #include "qapi/qapi-commands-machine.h"
> +#include "qobject/qdict.h"
>
>
> /* ----------------------------------------------------------------------- */
> @@ -167,7 +168,8 @@ static void handle_ovmf_log_range(GString *out,
> }
> }
>
> -FirmwareLog *qmp_query_firmware_log(Error **errp)
> +FirmwareLog *qmp_query_firmware_log(bool have_maxsize, uint64_t maxsize,
> + Error **errp)
> {
> MEM_DEBUG_LOG_HDR header;
> dma_addr_t offset, base;
> @@ -187,18 +189,38 @@ FirmwareLog *qmp_query_firmware_log(Error **errp)
> return NULL;
> }
>
> - if (header.DebugLogSize > MiB) {
> - /* default size is 128k (32 pages), allow up to 1M */
> - error_setg(errp, "firmware log: log buffer is too big");
> - return NULL;
> - }
> -
> if (header.DebugLogHeadOffset > header.DebugLogSize ||
> header.DebugLogTailOffset > header.DebugLogSize) {
> error_setg(errp, "firmware log: invalid header");
> return NULL;
> }
>
> + if (!have_maxsize) {
> + maxsize = MiB;
> + }
> + if (maxsize > MiB) {
> + maxsize = MiB;
Silently "fixing" the user's instructions is rarely a good idea. Either
don't limit the argument (if the user asks for rope...), or make
exceeding the limit an error.
> + }
> +
> + /* adjust header.DebugLogHeadOffset so we rezturn at most maxsize bytes */
> + if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
> + /* wrap around */
> + if (header.DebugLogTailOffset > maxsize) {
> + header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
> + } else {
> + uint64_t maxchunk = maxsize - header.DebugLogTailOffset;
> + if (header.DebugLogSize > maxchunk &&
> + header.DebugLogHeadOffset < header.DebugLogSize - maxchunk) {
> + header.DebugLogHeadOffset = header.DebugLogSize - maxchunk;
> + }
> + }
> + } else {
> + if (header.DebugLogTailOffset > maxsize &&
> + header.DebugLogHeadOffset < header.DebugLogTailOffset - maxsize) {
> + header.DebugLogHeadOffset = header.DebugLogTailOffset - maxsize;
> + }
> + }
> +
> base = offset + header.HeaderSize;
> if (header.DebugLogHeadOffset > header.DebugLogTailOffset) {
> /* wrap around */
> @@ -237,8 +259,10 @@ void hmp_info_firmware_log(Monitor *mon, const QDict *qdict)
> {
> Error *errp = NULL;
> FirmwareLog *log;
> + int64_t maxsize;
>
> - log = qmp_query_firmware_log(&errp);
> + maxsize = qdict_get_try_int(qdict, "maxsize", -1);
> + log = qmp_query_firmware_log(maxsize != -1, (uint64_t)maxsize, &errp);
Put a pin here.
> if (errp) {
> hmp_handle_error(mon, errp);
> return;
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 257015f0b403..db03d88d3c74 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -980,11 +980,10 @@ ERST
>
> {
> .name = "firmware-log",
> - .args_type = "",
> - .params = "",
> + .args_type = "maxsize:i?",
args_type 'i' is a 32 bit signed integer, so this gives us 31 bits.
Suffices. But what happens when the user specifies a negative number?
I think hmp_info_firmware_log() treats -1 as if the parameter was
omitted. qmp_query_firmware_log() then defaults to 1MiB. Any other
negative number hmp_info_firmware_log() turns into a huge positive
number, which qmp_query_firmware_log() silently limits to 1MiB (but I
recommended not to do that).
Let's use 'o' instead of 'i'. Enables convenient syntax like "64k". 63
bits. No risk of sign accidents.
> + .params = "[maxsize]",
> .help = "show the firmware (ovmf) debug log",
> .cmd = hmp_info_firmware_log,
> - .flags = "p",
Accident?
> },
>
> SRST
> diff --git a/qapi/machine.json b/qapi/machine.json
> index c96e582afdd6..d0c6d3ede027 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1857,9 +1857,12 @@
> #
> # Find firmware memory log buffer in guest memory, return content.
> #
> +# @maxsize: limit the amount of logdata returned.
Please spell it @max-size. We already use that spelling in this file.
"logdata" isn't a word.
The 1MiB limit for @maxsize needs to be documented (if we keep it).
Recommend to spell out that the command returns the tail of the log
buffer when it can't return all of it.
> +#
> # Since: 10.2
> ##
> { 'command': 'query-firmware-log',
> + 'data': { '*maxsize': 'size' },
> 'returns': 'FirmwareLog' }
>
> ##
On Mon, Oct 13, 2025 at 12:49:54PM +0200, Gerd Hoffmann wrote: > Allow limiting the amount of log output sent. Allow up to 1 MiB. > In case the guest log buffer is larger than 1 MiB limit the output > instead of throwing an error. > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> > --- > hw/uefi/ovmf-log.c | 40 ++++++++++++++++++++++++++++++++-------- > hmp-commands-info.hx | 5 ++--- > qapi/machine.json | 3 +++ > 3 files changed, 37 insertions(+), 11 deletions(-) Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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