[PATCH] libfile: implement new pread_full

[Ahmad Fatoum]

We already have pwrite_full, add pread_full for symmetry.

Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
---
 include/libfile.h |  1 +
 lib/libfile.c     | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/libfile.h b/include/libfile.h
index 3c2fe1714dcb..a353ccfa9ea9 100644
--- a/include/libfile.h
+++ b/include/libfile.h
@@ -2,6 +2,7 @@
 #ifndef __LIBFILE_H
 #define __LIBFILE_H
 
+int pread_full(int fd, void *buf, size_t size, loff_t offset);
 int pwrite_full(int fd, const void *buf, size_t size, loff_t offset);
 int write_full(int fd, const void *buf, size_t size);
 int read_full(int fd, void *buf, size_t size);
diff --git a/lib/libfile.c b/lib/libfile.c
index 6b373f05ca72..1f533133c593 100644
--- a/lib/libfile.c
+++ b/lib/libfile.c
@@ -75,6 +75,31 @@ int write_full(int fd, const void *buf, size_t size)
 }
 EXPORT_SYMBOL(write_full);
 
+/*
+ * 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;
+}
+EXPORT_SYMBOL(pread_full);
+
 /*
  * read_full - read from filedescriptor
  *
-- 
2.30.2