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Message-Id: <20250322-initrd-erofs-v2-3-d66ee4a2c756@cyberus-technology.de>
Date: Sat, 22 Mar 2025 21:34:15 +0100
From: Julian Stecklina via B4 Relay <devnull+julian.stecklina.cyberus-technology.de@...nel.org>
To: Christoph Hellwig <hch@....de>, Al Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J. Wysocki" <rafael@...nel.org>, Gao Xiang <xiang@...nel.org>,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-erofs@...ts.ozlabs.org,
Julian Stecklina <julian.stecklina@...erus-technology.de>
Subject: [PATCH v2 3/9] initrd: add a generic mechanism to add fs detectors
From: Julian Stecklina <julian.stecklina@...erus-technology.de>
So far all filesystems that are supported as initrd have their
filesystem detection code implemented in init/do_mounts_rd.c. A better
approach is to let filesystem implementations register a detection
hook. This allows the filesystem detection code to live with the rest
of the filesystem implementation.
We could have done a more flexible mechanism than passing a block of
data, but this simple solution works for all filesystems and keeps the
boilerplate low.
The following patches will convert each of the filesystems.
Suggested-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Julian Stecklina <julian.stecklina@...erus-technology.de>
---
include/asm-generic/vmlinux.lds.h | 6 ++++++
include/linux/initrd.h | 37 +++++++++++++++++++++++++++++++++++++
init/do_mounts_rd.c | 28 +++++++++++++++++++++++++++-
3 files changed, 70 insertions(+), 1 deletion(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 0d5b186abee86d27f3b02a49299155453a8c8e9e..d0816e6c41a9bbedf8f5a68c33b6f3e18014019a 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -968,8 +968,13 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
KEEP(*(.init.ramfs)) \
. = ALIGN(8); \
KEEP(*(.init.ramfs.info))
+
+#define INITRD_FS_DETECT() \
+ . = ALIGN(16); \
+ BOUNDED_SECTION(_initrd_fs_detect)
#else
#define INIT_RAM_FS
+#define INITRD_FS_DETECT()
#endif
/*
@@ -1170,6 +1175,7 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
INIT_CALLS \
CON_INITCALL \
INIT_RAM_FS \
+ INITRD_FS_DETECT() \
}
#define BSS_SECTION(sbss_align, bss_align, stop_align) \
diff --git a/include/linux/initrd.h b/include/linux/initrd.h
index f1a1f4c92ded3921bf56d53bee3e20b549d851fb..25463ce9c26ad4e4e9d3b333aa9f5596585c1762 100644
--- a/include/linux/initrd.h
+++ b/include/linux/initrd.h
@@ -3,6 +3,9 @@
#ifndef __LINUX_INITRD_H
#define __LINUX_INITRD_H
+#include <linux/init.h>
+#include <linux/types.h>
+
#define INITRD_MINOR 250 /* shouldn't collide with /dev/ram* too soon ... */
/* starting block # of image */
@@ -18,12 +21,46 @@ extern int initrd_below_start_ok;
extern unsigned long initrd_start, initrd_end;
extern void free_initrd_mem(unsigned long, unsigned long);
+struct file;
+
#ifdef CONFIG_BLK_DEV_INITRD
extern void __init reserve_initrd_mem(void);
extern void wait_for_initramfs(void);
+
+/*
+ * Detect a filesystem on the initrd. You get 1 KiB (BLOCK_SIZE) of
+ * data to work with. The offset of the block is specified in
+ * initrd_fs_detect().
+ *
+ * @block_data: A pointer to BLOCK_SIZE of data
+ *
+ * Returns the size of the filesystem in bytes or 0, if the filesystem
+ * was not detected.
+ */
+typedef size_t initrd_fs_detect_fn(void * const block_data);
+
+struct initrd_detect_fs {
+ initrd_fs_detect_fn *detect_fn;
+ loff_t detect_byte_offset;
+};
+
+extern struct initrd_detect_fs __start_initrd_fs_detect[];
+extern struct initrd_detect_fs __stop_initrd_fs_detect[];
+
+/*
+ * Add a filesystem detector for initrds. See the documentation of
+ * initrd_fs_detect_fn above.
+ */
+#define initrd_fs_detect(fn, byte_offset) \
+ static const struct initrd_detect_fs __initrd_fs_detect_ ## fn \
+ __used __section("_initrd_fs_detect") = \
+ { .detect_fn = fn, .detect_byte_offset = byte_offset}
+
#else
static inline void __init reserve_initrd_mem(void) {}
static inline void wait_for_initramfs(void) {}
+
+#define initrd_fs_detect(detectfn)
#endif
extern phys_addr_t phys_initrd_start;
diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index d026df401afa0b7458ab1f266b21830aab974b92..56c1fa935c7ee780870142923046a3d2fd2d6d96 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -58,7 +58,7 @@ static int __init
identify_ramdisk_image(struct file *file, loff_t pos,
decompress_fn *decompressor)
{
- const int size = 512;
+ const int size = BLOCK_SIZE;
struct minix_super_block *minixsb;
struct romfs_super_block *romfsb;
struct cramfs_super *cramfsb;
@@ -68,6 +68,7 @@ identify_ramdisk_image(struct file *file, loff_t pos,
const char *compress_name;
unsigned long n;
int start_block = rd_image_start;
+ struct initrd_detect_fs *detect_fs;
buf = kmalloc(size, GFP_KERNEL);
if (!buf)
@@ -165,6 +166,31 @@ identify_ramdisk_image(struct file *file, loff_t pos,
goto done;
}
+ /* Try to find a filesystem in the initrd */
+ for (detect_fs = __start_initrd_fs_detect;
+ detect_fs < __stop_initrd_fs_detect;
+ detect_fs++
+ ) {
+ size_t fs_size;
+
+ pos = (start_block * BLOCK_SIZE) + detect_fs->detect_byte_offset;
+ kernel_read(file, buf, size, &pos);
+
+ fs_size = detect_fs->detect_fn(buf);
+
+ if (fs_size == 0)
+ continue;
+
+ nblocks = (fs_size + BLOCK_SIZE + 1)
+ >> BLOCK_SIZE_BITS;
+
+ printk(KERN_NOTICE
+ "RAMDISK: filesystem found (%d blocks)\n",
+ nblocks);
+
+ goto done;
+ }
+
printk(KERN_NOTICE
"RAMDISK: Couldn't find valid RAM disk image starting at %d.\n",
start_block);
--
2.47.0
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