[dmidecode] [PATCH 1/4] add read_file() function for reading sysfs files

[Roy Franz]

Add a function that can read a complete, unknown size file for
reading entry point files from sysfs.  This function models its signature
on the mem_chunk() funtion, so it also allocates memory that the caller
needs to free.  The files that we are interested in reading are very small,
and have a known upper bound on the size.  The EINTR handling is based
on the myread() function.

Signed-off-by: Roy Franz <address@hidden>
---
 util.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 util.h |  1 +
 2 files changed, 51 insertions(+)

diff --git a/util.c b/util.c
index 2ab4915..8acc8f5 100644
--- a/util.c
+++ b/util.c
@@ -77,6 +77,56 @@ static int myread(int fd, u8 *buf, size_t count, const char 
*prefix)
 
        return 0;
 }
+/*
+ * Reads all of file, up to len bytes.
+ * A buffer of len bytes is allocated by this function, and
+ * needs to be freed by the caller.
+ * This provides a similar usage model to mem_chunk()
+ *
+ * Returns pointer to buffer of len bytes, or NULL on error
+ *
+ */
+void *read_file(size_t len, const char *filename)
+{
+       int fd;
+       size_t r2 = 0;
+       ssize_t r;
+       u8 *p;
+
+       /*
+        * Don't print error message on missing file, as we will try to read
+        * files that may or may not be present.
+        */
+       if ((fd = open(filename, O_RDONLY)) == -1)
+               return NULL;
+
+       if ((p = malloc(len)) == NULL)
+       {
+               perror("malloc");
+               return NULL;
+       }
+
+       do
+       {
+               r = read(fd, p + r2, len - r2);
+               if (r == -1)
+               {
+                       if (errno != EINTR)
+                       {
+                               close(fd);
+                               perror(filename);
+                               free(p);
+                               return NULL;
+                       }
+               }
+               else
+                       r2 += r;
+       }
+       while (r != 0);
+
+       close(fd);
+       return p;
+}
 
 int checksum(const u8 *buf, size_t len)
 {
diff --git a/util.h b/util.h
index e564292..ca8080e 100644
--- a/util.h
+++ b/util.h
@@ -28,3 +28,4 @@ int checksum(const u8 *buf, size_t len);
 void *mem_chunk(size_t base, size_t len, const char *devmem);
 int write_dump(size_t base, size_t len, const void *data, const char 
*dumpfile, int add);
 u64 u64_range(u64 start, u64 end);
+void *read_file(size_t len, const char *filename);
-- 
1.9.1