[PATCH] lib: fwts_acpi_tables: don't do expensive low allocs multiple times

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

fwts_low_realloc is quite an expensive operation and multiple reallocs
should be avoided.  Instead, temporarily allocate the table using the
conventional realloc heap and use low memory allocation at the end once
we know the full table size.

Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 src/lib/src/fwts_acpi_tables.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/lib/src/fwts_acpi_tables.c b/src/lib/src/fwts_acpi_tables.c
index fd2c85d..0191b6b 100644
--- a/src/lib/src/fwts_acpi_tables.c
+++ b/src/lib/src/fwts_acpi_tables.c
@@ -720,15 +720,19 @@ static int fwts_acpi_load_tables_from_acpidump(fwts_framework *fw)
  */
 static uint8_t *fwts_acpi_load_table_from_file(const int fd, size_t *length)
 {
-	uint8_t *ptr = NULL;
+	uint8_t *ptr = NULL, *tmp;
 	size_t size = 0;
 	char buffer[4096];
 
 	*length = 0;
 
+	/*
+	 *  read table into buffer in the normal heap
+	 *  so we don't have to do expensive fwts_low_reallocs
+	 *  per iteration on long tables
+	 */
 	for (;;) {
 		ssize_t n = read(fd, buffer, sizeof(buffer));
-		uint8_t *tmp;
 
 		if (n == 0)
 			break;
@@ -740,11 +744,11 @@ static uint8_t *fwts_acpi_load_table_from_file(const int fd, size_t *length)
 			continue;
 		}
 		if (n > (ssize_t)sizeof(buffer))
-			goto too_big;	/* Unlikely */
+			goto err;	/* Unlikely */
 		if (size + n > 0xffffffff)
-			goto too_big;	/* Very unlikely */
+			goto err;	/* Very unlikely */
 
-		if ((tmp = (uint8_t*)fwts_low_realloc(ptr, size + n + 1)) == NULL) {
+		if ((tmp = (uint8_t*)realloc(ptr, size + n + 1)) == NULL) {
 			free(ptr);
 			return NULL;
 		}
@@ -752,10 +756,19 @@ static uint8_t *fwts_acpi_load_table_from_file(const int fd, size_t *length)
 		memcpy(ptr + size, buffer, n);
 		size += n;
 	}
+
+	/*
+	 *  ..and copy table into a 32 bit memory space buffer
+	 */
+	if ((tmp = fwts_low_malloc(size)) == NULL)
+		goto err;
+
 	*length = size;
-	return ptr;
+	memcpy(tmp, ptr, size);
+	free(ptr);
+	return tmp;
 
-too_big:
+err:
 	free(ptr);
 	*length = 0;
 	return NULL;
-- 
2.7.0.rc3