[PATCH v3 0/4] enhance error handling in kvmppc_read_int*

[PATCH v3 0/4] enhance error handling in kvmppc_read_int*

[Daniel Henrique Barboza]

Hi,

In this v3 I changed the error report after fopen() to use
error_setg_errno(), as suggested by Cedric.

I also cut patch 1/1 because it's simpler to do all the function changes
in a single patch instead of having a separated patch just to change the
return value of both.

Changes from v2:
- former patch 1/1: dropped
- patch 1 (former 3):
  - use error_setg_errno() instead of error_setg() 
- v2 link: https://lists.gnu.org/archive/html/qemu-devel/2022-07/msg01167.html

Daniel Henrique Barboza (3):
  target/ppc: enhance error report in kvmppc_read_int_cpu_dt()
  target/ppc: use g_autofree in kvmppc_read_int_cpu_dt()
  target/ppc: exit(1) on failure in kvmppc_get_clockfreq()

jianchunfu (1):
  target/ppc: add error report when fopen fails in kvmppc_read_int_dt()

 target/ppc/kvm.c | 46 +++++++++++++++++++++++++++++++---------------
 1 file changed, 31 insertions(+), 15 deletions(-)

-- 
2.36.1

[PATCH v3 1/4] target/ppc: add error report when fopen fails in kvmppc_read_int_dt()

[Daniel Henrique Barboza]

From: jianchunfu <jianchunfu@cmss.chinamobile.com>

Use an Error pointer to report the error back to the caller.

While we're at it, return '0' instead of '-1' on error since the
function is supposed to return an uint64_t.

Signed-off-by: jianchunfu <jianchunfu@cmss.chinamobile.com>
[danielhb: return 0, use error_set_errno() instead of fprintf]
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/kvm.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 6eed466f80..65d136ed5a 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -1896,7 +1896,7 @@ static int kvmppc_find_cpu_dt(char *buf, int buf_len)
     return 0;
 }
 
-static uint64_t kvmppc_read_int_dt(const char *filename)
+static uint64_t kvmppc_read_int_dt(const char *filename, Error **errp)
 {
     union {
         uint32_t v32;
@@ -1907,7 +1907,8 @@ static uint64_t kvmppc_read_int_dt(const char *filename)
 
     f = fopen(filename, "rb");
     if (!f) {
-        return -1;
+        error_setg_errno(errp, errno, "error opening %s", filename);
+        return 0;
     }
 
     len = fread(&u, 1, sizeof(u), f);
@@ -1938,7 +1939,7 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname)
     }
 
     tmp = g_strdup_printf("%s/%s", buf, propname);
-    val = kvmppc_read_int_dt(tmp);
+    val = kvmppc_read_int_dt(tmp, NULL);
     g_free(tmp);
 
     return val;
-- 
2.36.1

[PATCH v3 2/4] target/ppc: enhance error report in kvmppc_read_int_cpu_dt()

[Daniel Henrique Barboza]

First and foremost, the function can't return '-1' when an error occurs
because the return type is set to uint64_t. Let's fix that.

After that, the function can't simply return 0 whether an error happened
and call it a day. We must provide a way of letting callers know if the
zero return is legitimate or due to an error.

Add an Error pointer to kvmppc_read_int_cpu_dt() that will be filled
with an appropriate error, if one occurs. Callers are then free to pass
an Error pointer and handle it.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/kvm.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 65d136ed5a..cf4610b6fa 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -1926,20 +1926,22 @@ static uint64_t kvmppc_read_int_dt(const char *filename, Error **errp)
 
 /*
  * Read a CPU node property from the host device tree that's a single
- * integer (32-bit or 64-bit).  Returns 0 if anything goes wrong
- * (can't find or open the property, or doesn't understand the format)
+ * integer (32-bit or 64-bit).  Returns 0 and set errp if anything goes
+ * wrong (can't find or open the property, or doesn't understand the
+ * format)
  */
-static uint64_t kvmppc_read_int_cpu_dt(const char *propname)
+static uint64_t kvmppc_read_int_cpu_dt(const char *propname, Error **errp)
 {
     char buf[PATH_MAX], *tmp;
     uint64_t val;
 
     if (kvmppc_find_cpu_dt(buf, sizeof(buf))) {
-        return -1;
+        error_setg(errp, "Failed to read CPU property %s", propname);
+        return 0;
     }
 
     tmp = g_strdup_printf("%s/%s", buf, propname);
-    val = kvmppc_read_int_dt(tmp, NULL);
+    val = kvmppc_read_int_dt(tmp, errp);
     g_free(tmp);
 
     return val;
@@ -1947,12 +1949,12 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname)
 
 uint64_t kvmppc_get_clockfreq(void)
 {
-    return kvmppc_read_int_cpu_dt("clock-frequency");
+    return kvmppc_read_int_cpu_dt("clock-frequency", NULL);
 }
 
 static int kvmppc_get_dec_bits(void)
 {
-    int nr_bits = kvmppc_read_int_cpu_dt("ibm,dec-bits");
+    int nr_bits = kvmppc_read_int_cpu_dt("ibm,dec-bits", NULL);
 
     if (nr_bits > 0) {
         return nr_bits;
@@ -2337,8 +2339,8 @@ static void alter_insns(uint64_t *word, uint64_t flags, bool on)
 static void kvmppc_host_cpu_class_init(ObjectClass *oc, void *data)
 {
     PowerPCCPUClass *pcc = POWERPC_CPU_CLASS(oc);
-    uint32_t dcache_size = kvmppc_read_int_cpu_dt("d-cache-size");
-    uint32_t icache_size = kvmppc_read_int_cpu_dt("i-cache-size");
+    uint32_t dcache_size = kvmppc_read_int_cpu_dt("d-cache-size", NULL);
+    uint32_t icache_size = kvmppc_read_int_cpu_dt("i-cache-size", NULL);
 
     /* Now fix up the class with information we can query from the host */
     pcc->pvr = mfpvr();
-- 
2.36.1

[PATCH v3 3/4] target/ppc: use g_autofree in kvmppc_read_int_cpu_dt()

[Daniel Henrique Barboza]

This spares us a g_free() call. Let's also not use 'val' and return the
value of kvmppc_read_int_dt() directly.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/kvm.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index cf4610b6fa..37a312288d 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -1932,8 +1932,8 @@ static uint64_t kvmppc_read_int_dt(const char *filename, Error **errp)
  */
 static uint64_t kvmppc_read_int_cpu_dt(const char *propname, Error **errp)
 {
-    char buf[PATH_MAX], *tmp;
-    uint64_t val;
+    g_autofree char *tmp = NULL;
+    char buf[PATH_MAX];
 
     if (kvmppc_find_cpu_dt(buf, sizeof(buf))) {
         error_setg(errp, "Failed to read CPU property %s", propname);
@@ -1941,10 +1941,8 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname, Error **errp)
     }
 
     tmp = g_strdup_printf("%s/%s", buf, propname);
-    val = kvmppc_read_int_dt(tmp, errp);
-    g_free(tmp);
 
-    return val;
+    return kvmppc_read_int_dt(tmp, errp);
 }
 
 uint64_t kvmppc_get_clockfreq(void)
-- 
2.36.1

[PATCH v3 4/4] target/ppc: exit(1) on failure in kvmppc_get_clockfreq()

[Daniel Henrique Barboza]

When running under KVM accel it is expected to have 'clock-frequency' in
the DT. Not having this attribute is too risky for both the machine
emulation and userspace.

We have a way of telling whether this error scenario might happen or not
via kvmppc_read_int_cpu_dt() now being able to report errors. From now
on, when running KVM, we will assume that 'clock-frequency' will always
be present in the DT.

Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 target/ppc/kvm.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index 37a312288d..14faa14da3 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -1945,9 +1945,24 @@ static uint64_t kvmppc_read_int_cpu_dt(const char *propname, Error **errp)
     return kvmppc_read_int_dt(tmp, errp);
 }
 
+/*
+ * Read the clock-frequency from the DT. On error (e.g.
+ * 'clock-frequency' is not present in the DT) will
+ * report an error and exit(1).
+ */
 uint64_t kvmppc_get_clockfreq(void)
 {
-    return kvmppc_read_int_cpu_dt("clock-frequency", NULL);
+    Error *local_err = NULL;
+    int ret;
+
+    ret = kvmppc_read_int_cpu_dt("clock-frequency", &local_err);
+
+    if (local_err) {
+        error_report_err(local_err);
+        exit(1);
+    }
+
+    return ret;
 }
 
 static int kvmppc_get_dec_bits(void)
-- 
2.36.1