Re: [PATCH v2 08/13] util/hexdump: Have qemu_hexdump_line() return heap allocated buffer

[Richard Henderson]

On 4/11/24 03:15, Philippe Mathieu-Daudé wrote:

Signed-off-by: Philippe Mathieu-Daudé <phi...@linaro.org>
---
  include/qemu/cutils.h  | 10 +++++++---
  hw/virtio/vhost-vdpa.c |  5 +++--
  util/hexdump.c         | 12 ++++++++----
  3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
index 70ca4b876b..e8d6b86098 100644
--- a/include/qemu/cutils.h
+++ b/include/qemu/cutils.h
@@ -254,18 +254,22 @@ int parse_debug_env(const char *name, int max, int 
initial);

/**

   * qemu_hexdump_line:
- * @line: Buffer to be filled by the hexadecimal/ASCII dump
   * @bufptr: Buffer to dump
   * @offset: Offset within @bufptr to start the dump
   * @len: Length of the bytes do dump
   * @ascii: Replace non-ASCII characters by the dot symbol
   *
   * Hexdump a line of a byte buffer into a hexadecimal/ASCII buffer
+ *
+ * The caller must use g_free() to free the returned data when it is
+ * no longer required.
+ *
+ * Returns: Hexadecimal/ASCII dump
   */
  #define QEMU_HEXDUMP_LINE_BYTES 16 /* Number of bytes to dump */
  #define QEMU_HEXDUMP_LINE_LEN 75   /* Number of characters in line */
-void qemu_hexdump_line(char *line, const void *bufptr, unsigned offset,
-                       unsigned int len, bool ascii);
+char *qemu_hexdump_line(const void *bufptr, unsigned offset,
+                        unsigned int len, bool ascii);

/*

   * Hexdump a buffer to a file. An optional string prefix is added to every 
line
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index cf7cfa3f16..e61af86d9d 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -942,12 +942,13 @@ static void vhost_vdpa_dump_config(struct vhost_dev *dev, 
const uint8_t *config,
                                     uint32_t config_len)
  {
      int ofs, len;
-    char line[QEMU_HEXDUMP_LINE_LEN];
+    char *line;

for (ofs = 0; ofs < config_len; ofs += 16) {

          len = config_len - ofs;
-        qemu_hexdump_line(line, config, ofs, len, false);
+        line = qemu_hexdump_line(config, ofs, len, false);
          trace_vhost_vdpa_dump_config(dev, line);
+        g_free(line);
      }
  }

diff --git a/util/hexdump.c b/util/hexdump.c

index 469083d8c0..b6f70e93bb 100644
--- a/util/hexdump.c
+++ b/util/hexdump.c
@@ -16,9 +16,10 @@
  #include "qemu/osdep.h"
  #include "qemu/cutils.h"

-void qemu_hexdump_line(char *line, const void *bufptr, unsigned offset,

-                       unsigned int len, bool ascii)
+char *qemu_hexdump_line(const void *bufptr, unsigned offset,
+                        unsigned int len, bool ascii)
  {
+    char linebuf[QEMU_HEXDUMP_LINE_BYTES], *line = linebuf;
      const char *buf = bufptr;
      int i, c;

@@ -48,18 +49,21 @@ void qemu_hexdump_line(char *line, const void *bufptr, unsigned offset,

          }
      }
      *line = '\0';
+
+    return g_strdup(linebuf);
  }

void qemu_hexdump(FILE *fp, const char *prefix,

                    const void *bufptr, size_t size)
  {
      unsigned int ofs, len;
-    char line[QEMU_HEXDUMP_LINE_LEN];
+    char *line;

for (ofs = 0; ofs < size; ofs += QEMU_HEXDUMP_LINE_BYTES) {

          len = size - ofs;
-        qemu_hexdump_line(line, bufptr, ofs, len, true);
+        line = qemu_hexdump_line(bufptr, ofs, len, true);
          fprintf(fp, "%s: %s\n", prefix, line);
+        g_free(line);
      }

}

Not especially efficient, re-allocating for each line.

How about

GString *qemu_hexdump_line(GString *str, buf, offset, len, ascii)
{
    if (str) {
        g_string_truncate(str, 0);
    } else {
        str = g_string_sized_new(QEMU_HEXDUMP_LINE_LEN);
    }
    ...
    return str;
}

void qemu_hexdump(FILE *fp, ...)
{
    g_autoptr(GString) str = g_string_sized_new(QEMU_HEXDUMP_LINE_LEN);

    for (...) {
        qemu_hexdump_line(str, ...);
        fprintf(fp, "%s: %s\n", prefix, str->str);
    }
}

So that we reuse the one allocation across the whole loop.

r~