@@ -14,10 +14,10 @@ is different. The initramfs buffer contains an archive which is
expanded into a ramfs filesystem; this document details the format of
the initramfs buffer format.
-The initramfs buffer format is based around the "newc" or "crc" CPIO
-formats, and can be created with the cpio(1) utility. The cpio
-archive can be compressed using gzip(1). One valid version of an
-initramfs buffer is thus a single .cpio.gz file.
+The initramfs buffer format is based around the "newc" CPIO format, and
+can be created with the cpio(1) utility. The cpio archive can be
+compressed using gzip(1). One valid version of an initramfs buffer is
+thus a single .cpio.gz file.
The full format of the initramfs buffer is defined by the following
grammar, where::
@@ -40,9 +40,8 @@ grammar, where::
In human terms, the initramfs buffer contains a collection of
-compressed and/or uncompressed cpio archives (in the "newc" or "crc"
-formats); arbitrary amounts zero bytes (for padding) can be added
-between members.
+compressed and/or uncompressed cpio archives (in the "newc" format),
+with arbitrary amount of zero-byte padding between members.
The cpio "TRAILER!!!" entry (cpio end-of-archive) is optional, but is
not ignored; see "handling of hard links" below.
@@ -55,7 +54,7 @@ by the ASCII string "000012ac"):
============= ================== ==============================================
Field name Field size Meaning
============= ================== ==============================================
-c_magic 6 bytes The string "070701" or "070702"
+c_magic 6 bytes The string "070701"
c_ino 8 bytes File inode number
c_mode 8 bytes File mode and permissions
c_uid 8 bytes File uid
@@ -68,8 +67,7 @@ c_min 8 bytes Minor part of file device number
c_rmaj 8 bytes Major part of device node reference
c_rmin 8 bytes Minor part of device node reference
c_namesize 8 bytes Length of filename, including final \0
-c_chksum 8 bytes Checksum of data field if c_magic is 070702;
- otherwise zero
+c_chksum 8 bytes Ignored; reserved for unsupported "crc" format
============= ================== ==============================================
The c_mode field matches the contents of st_mode returned by stat(2)
@@ -78,12 +76,6 @@ on Linux, and encodes the file type and file permissions.
The c_filesize should be zero for any file which is not a regular file
or symlink.
-The c_chksum field contains a simple 32-bit unsigned sum of all the
-bytes in the data field. cpio(1) refers to this as "crc", which is
-clearly incorrect (a cyclic redundancy check is a different and
-significantly stronger integrity check), however, this is the
-algorithm used.
-
If the filename is "TRAILER!!!" this is actually an end-of-archive
marker; the c_filesize for an end-of-archive marker must be zero.
init/initramfs.c only supports extraction of cpio archives carrying the "newc" header magic ("070701"). Remove statements indicating support for the "crc" cpio format. Signed-off-by: David Disseldorp <ddiss@suse.de> --- .../early-userspace/buffer-format.rst | 24 +++++++------------ 1 file changed, 8 insertions(+), 16 deletions(-) Version 2: - reword initramfs padding description, as suggested by Matthew Wilcox