[PATCH v3 6/9] initramfs: merge header_buf and name_buf

[David Disseldorp <ddiss@xxxxxxx>]

header_buf is only used in FSM states up to GotHeader, while name_buf is
only used in states following GotHeader (Collect is shared, but the
collect pointer tracks each buffer). These buffers can therefore be
combined into a single cpio_buf, which can be used for both header and
file name storage.

Signed-off-by: David Disseldorp <ddiss@xxxxxxx>
---
 init/initramfs.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/init/initramfs.c b/init/initramfs.c
index 59b4a43fa491b..4e2506a4bc76f 100644
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -250,11 +250,11 @@ static void __init read_into(char *buf, unsigned size, enum state next)
 	}
 }
 
-static __initdata char *header_buf, *name_buf;
+static __initdata char *cpio_buf;
 
 static int __init do_start(void)
 {
-	read_into(header_buf, CPIO_HDRLEN, GotHeader);
+	read_into(cpio_buf, CPIO_HDRLEN, GotHeader);
 	return 0;
 }
 
@@ -294,14 +294,14 @@ static int __init do_header(void)
 	if (S_ISLNK(mode)) {
 		if (body_len > PATH_MAX)
 			return 0;
-		collect = collected = name_buf;
+		collect = collected = cpio_buf;
 		remains = N_ALIGN(name_len) + body_len;
 		next_state = GotSymlink;
 		state = Collect;
 		return 0;
 	}
 	if (S_ISREG(mode) || !body_len)
-		read_into(name_buf, N_ALIGN(name_len), GotName);
+		read_into(cpio_buf, N_ALIGN(name_len), GotName);
 	return 0;
 }
 
@@ -511,11 +511,16 @@ char * __init unpack_to_rootfs(char *buf, unsigned long len)
 	const char *compress_name;
 	static __initdata char msg_buf[64];
 
-	header_buf = kmalloc(CPIO_HDRLEN, GFP_KERNEL);
-	/* 2x PATH_MAX as @name_buf is also used for staging symlink targets */
-	name_buf = kmalloc(N_ALIGN(PATH_MAX) + PATH_MAX + 1, GFP_KERNEL);
-	if (!header_buf || !name_buf)
-		panic_show_mem("can't allocate buffers");
+	/*
+	 * @cpio_buf can be used for staging the 110 byte newc/crc cpio header,
+	 * after which parse_header() converts and stashes fields into
+	 * corresponding types. The same buffer can then be reused for file
+	 * path staging. 2 x PATH_MAX covers any possible symlink target.
+	 */
+	BUILD_BUG_ON(CPIO_HDRLEN > N_ALIGN(PATH_MAX) + PATH_MAX + 1);
+	cpio_buf = kmalloc(N_ALIGN(PATH_MAX) + PATH_MAX + 1, GFP_KERNEL);
+	if (!cpio_buf)
+		panic_show_mem("can't allocate buffer");
 
 	state = Start;
 	this_header = 0;
@@ -559,8 +564,7 @@ char * __init unpack_to_rootfs(char *buf, unsigned long len)
 		len -= my_inptr;
 	}
 	dir_utime();
-	kfree(name_buf);
-	kfree(header_buf);
+	kfree(cpio_buf);
 	return message;
 }
 
-- 
2.43.0