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Add comments to initramfs.c #1061

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Add comments to initramfs.c #1061

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30 changes: 30 additions & 0 deletions init/initramfs.c
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Original file line number Diff line number Diff line change
@@ -1,3 +1,8 @@
/*
* This file contains the implementation of the initramfs, which is a temporary root filesystem used during the Linux kernel boot process.
* It is responsible for unpacking and populating the root filesystem from the initramfs image.
*/

// SPDX-License-Identifier: GPL-2.0
#include <linux/init.h>
#include <linux/async.h>
Expand All @@ -24,6 +29,11 @@
static __initdata bool csum_present;
static __initdata u32 io_csum;

/*
* Write data to a file.
* This function writes the specified data to the given file, updating the file position.
* If checksum calculation is enabled, it updates the checksum as well.
*/
static ssize_t __init xwrite(struct file *file, const unsigned char *p,
size_t count, loff_t *pos)
{
Expand Down Expand Up @@ -578,6 +588,10 @@ extern unsigned long __initramfs_size;

static BIN_ATTR(initrd, 0440, sysfs_bin_attr_simple_read, NULL, 0);

/*
* Reserve memory for the initrd.
* This function reserves the memory region for the initrd, ensuring it is not used for other purposes.
*/
void __init reserve_initrd_mem(void)
{
phys_addr_t start;
Expand Down Expand Up @@ -623,6 +637,10 @@ void __init reserve_initrd_mem(void)
initrd_end = 0;
}

/*
* Free the memory used by the initrd.
* This function releases the memory region used by the initrd, making it available for other purposes.
*/
void __weak __init free_initrd_mem(unsigned long start, unsigned long end)
{
#ifdef CONFIG_ARCH_KEEP_MEMBLOCK
Expand Down Expand Up @@ -688,6 +706,10 @@ static void __init populate_initrd_image(char *err)
}
#endif /* CONFIG_BLK_DEV_RAM */

/*
* Populate the root filesystem.
* This function populates the root filesystem by unpacking the initramfs image.
*/
static void __init do_populate_rootfs(void *unused, async_cookie_t cookie)
{
/* Load the built in initramfs */
Expand Down Expand Up @@ -736,6 +758,10 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie)
static ASYNC_DOMAIN_EXCLUSIVE(initramfs_domain);
static async_cookie_t initramfs_cookie;

/*
* Wait for the initramfs to be populated.
* This function waits for the initramfs to be fully populated before proceeding.
*/
void wait_for_initramfs(void)
{
if (!initramfs_cookie) {
Expand All @@ -752,6 +778,10 @@ void wait_for_initramfs(void)
}
EXPORT_SYMBOL_GPL(wait_for_initramfs);

/*
* Populate the root filesystem.
* This function schedules the population of the root filesystem by unpacking the initramfs image.
*/
static int __init populate_rootfs(void)
{
initramfs_cookie = async_schedule_domain(do_populate_rootfs, NULL,
Expand Down