[3/3] docs: remove mention of "crc" cpio format support

Commit Message

David Disseldorp June 10, 2021, 9:45 p.m. UTC

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 <[e-mail]>
---
 .../early-userspace/buffer-format.rst         | 25 +++++++------------
 1 file changed, 9 insertions(+), 16 deletions(-)

Comments

Matthew Wilcox June 10, 2021, 10:01 p.m. UTC | #1

On Thu, Jun 10, 2021 at 11:45:25PM +0200, David Disseldorp wrote:
> @@ -40,9 +40,9 @@ 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);
> +arbitrary amounts zero bytes (for padding) can be added between
> +members.

"arbitrary amounts of zero bytes", but even that doesn't sound quite
right.  Maybe "arbitrary amount of zero-byte padding between members"?

David Disseldorp June 10, 2021, 10:17 p.m. UTC | #2

On Thu, 10 Jun 2021 23:01:23 +0100, Matthew Wilcox wrote:

> >  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);
> > +arbitrary amounts zero bytes (for padding) can be added between
> > +members.  
> 
> "arbitrary amounts of zero bytes", but even that doesn't sound quite
> right.  Maybe "arbitrary amount of zero-byte padding between members"?

Your suggestion sounds good to me. Can I squash it in with this change
for a v2, or would you prefer to handle it as a separate grammar fix?

Cheers, David

Patch

diff --git a/Documentation/driver-api/early-userspace/buffer-format.rst b/Documentation/driver-api/early-userspace/buffer-format.rst
index 7f74e301fdf3..95e66606b605 100644
--- a/Documentation/driver-api/early-userspace/buffer-format.rst
+++ b/Documentation/driver-api/early-userspace/buffer-format.rst
@@ -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 +40,9 @@  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);
+arbitrary amounts zero bytes (for padding) can be added between
+members.
 
 The cpio "TRAILER!!!" entry (cpio end-of-archive) is optional, but is
 not ignored; see "handling of hard links" below.
@@ -55,7 +55,7 @@  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 +68,7 @@  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 +77,6 @@  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.