[PATCH] scripts: implement read_fd and pread_full for tools

[Ahmad Fatoum]

This will be useful for host/target tools that use stdin as
a fall back to read from when no file name is supplied.

Code is taken from the barebox version in lib/libfile.c.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 scripts/common.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++
 scripts/common.h |  2 ++
 2 files changed, 70 insertions(+)

diff --git a/scripts/common.c b/scripts/common.c
index 49c468a1ea35..a6eee968b79d 100644
--- a/scripts/common.c
+++ b/scripts/common.c
@@ -97,6 +97,50 @@ void *read_file(const char *filename, size_t *size)
 	return NULL;
 }
 
+/**
+ * read_fd - read from a file descriptor to an allocated buffer
+ * @filename:  The file descriptor to read
+ * @size:      After successful return contains the size of the file
+ *
+ * This function reads a file descriptor from offset 0 until EOF to an
+ * allocated buffer.
+ *
+ * Return: On success, returns a nul-terminated buffer with the file's
+ * contents that should be deallocated with free().
+ * On error, NULL is returned and errno is set to an error code.
+ */
+void *read_fd(int fd, size_t *out_size)
+{
+	struct stat st;
+	ssize_t ret;
+	void *buf;
+
+	ret = fstat(fd, &st);
+	if (ret < 0)
+		return NULL;
+
+	/* For user convenience, we always nul-terminate the buffer in
+	 * case it contains a string. As we don't want to assume the string
+	 * to be either an array of char or wchar_t, we just unconditionally
+	 * add 2 bytes as terminator. As the two byte terminator needs to be
+	 * aligned, we just make it three bytes
+	 */
+	buf = malloc(st.st_size + 3);
+	if (!buf)
+		return NULL;
+
+	ret = pread_full(fd, buf, st.st_size, 0);
+	if (ret < 0) {
+		free(buf);
+		return NULL;
+	}
+
+	memset(buf + st.st_size, '\0', 3);
+	*out_size = st.st_size;
+
+	return buf;
+}
+
 int write_file(const char *filename, const void *buf, size_t size)
 {
 	int fd, ret = 0;
@@ -147,6 +191,30 @@ int read_full(int fd, void *buf, size_t size)
 	return insize;
 }
 
+/*
+ * pread_full - read to filedescriptor at offset
+ *
+ * Like pread, but this function only returns less bytes than
+ * requested when the end of file is reached.
+ */
+int pread_full(int fd, void *buf, size_t size, loff_t offset)
+{
+	size_t insize = size;
+	int now;
+
+	while (size) {
+		now = pread(fd, buf, size, offset);
+		if (now == 0)
+			break;
+		if (now < 0)
+			return now;
+		size -= now;
+		buf += now;
+	}
+
+	return insize - size;
+}
+
 int write_full(int fd, const void *buf, size_t size)
 {
 	size_t insize = size;
diff --git a/scripts/common.h b/scripts/common.h
index 399729c338f3..a0d16606b5d9 100644
--- a/scripts/common.h
+++ b/scripts/common.h
@@ -3,8 +3,10 @@
 
 int read_file_2(const char *filename, size_t *size, void **outbuf, size_t max_size);
 void *read_file(const char *filename, size_t *size);
+void *read_fd(int fd, size_t *out_size);
 int write_file(const char *filename, const void *buf, size_t size);
 int read_full(int fd, void *buf, size_t size);
+int pread_full(int fd, void *buf, size_t size, loff_t offset);
 int write_full(int fd, const void *buf, size_t size);
 
 #endif /* __COMMON_H */
-- 
2.39.5