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[cpio] Allow for construction of parent directories as needed

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iPXE allows individual raw files to be automatically wrapped with
suitable CPIO headers and injected into the magic initrd image as
exposed to a booted Linux kernel.  This feature is currently limited
to placing files within directories that already exist in the initrd
filesystem.

Remove this limitation by adding the ability for iPXE to construct
CPIO headers for parent directories as needed, under control of the
"mkdir=<n>" command-line argument.  For example:

  initrd config.ign /usr/share/oem/config.ign mkdir=1

will create CPIO headers for the "/usr/share/oem" directory as well as
for the "/usr/share/oem/config.ign" file itself.

This simplifies the process of booting operating systems such as
Flatcar Linux, which otherwise require the single "config.ign" file to
be manually wrapped up as a CPIO archive solely in order to create the
relevant parent directory entries.

The value <n> may be used to control the number of parent directory
entries that are created.  For example, "mkdir=2" would cause up to
two parent directories to be created (i.e. "/usr/share" and
"/usr/share/oem" in the above example).  A negative value such as
"mkdir=-1" may be used to create all parent directories up to the root
of the tree.

Do not create any parent directory entries by default, since doing so
would potentially cause the modes and ownership information for
existing directories to be overwritten.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2025-02-24 14:04:06 +00:00
parent e7595fe88d
commit 12ea8c4074
4 changed files with 161 additions and 52 deletions
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25
src/include/ipxe/cpio.h
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@@ -9,6 +9,7 @@
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <stdint.h>
#include <ipxe/image.h>
/** A CPIO archive header
@@ -50,6 +51,12 @@ struct cpio_header {
/** CPIO magic */
#define CPIO_MAGIC "070701"
/** CPIO type for regular files */
#define CPIO_MODE_FILE 0100000
/** CPIO type for directories */
#define CPIO_MODE_DIR 0040000
/** CPIO header length alignment */
#define CPIO_ALIGN 4
@@ -67,8 +74,20 @@ cpio_name ( struct image *image ) {
return image->cmdline;
}
extern void cpio_set_field ( char *field, unsigned long value );
extern size_t cpio_name_len ( struct image *image );
extern size_t cpio_header ( struct image *image, struct cpio_header *cpio );
/**
* Get CPIO header zero-padding length
*
* @v len Length of CPIO header (including name, excluding NUL)
* @ret pad_len Padding length
*/
static inline __attribute__ (( always_inline )) size_t
cpio_pad_len ( size_t len ) {
/* Pad by at least one byte (for name's terminating NUL) */
return ( CPIO_ALIGN - ( len % CPIO_ALIGN ) );
}
extern size_t cpio_header ( struct image *image, unsigned int index,
struct cpio_header *cpio );
#endif /* _IPXE_CPIO_H */