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Message-Id: <20080903152231.6b82d9bf.akpm@linux-foundation.org>
Date: Wed, 3 Sep 2008 15:22:31 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Nye Liu <nyet@...t.org>
Cc: linux-kernel@...r.kernel.org, nyet@....com
Subject: Re: [PATCH] INITRAMFS: Add option to preserve mtime from INITRAMFS
cpio images
On Wed, 3 Sep 2008 13:29:38 -0700
Nye Liu <nyet@...t.org> wrote:
> Resubmission of initramfs preserve mtime patch following Andrew Morton's
> suggestions.
It's nice to provide some sort of accounting for the reviewer's
individual comments. But in this case I only had three or fopur and I
see how they were addressed.
> From: Nye Liu <nyet@...t.org>
>
> When unpacking the cpio into the initramfs, mtimes are not preserved by
> default. This patch adds an INITRAMFS_PRESERVE_MTIME option that allows mtimes
> stored in the cpio image to be used when constructing the initramfs. For
> embedded applications that run exclusively out of the initramfs, this is
> invaluable.
Why is it "invlauable". Please explain this value in full detail -
it's the whole reason for merging the patch!
> Signed-off-by: Nye Liu <nyet@...t.org>
>
> diff --git a/init/initramfs.c b/init/initramfs.c
> index 644fc01..ebfc049 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -6,6 +6,7 @@
> #include <linux/delay.h>
> #include <linux/string.h>
> #include <linux/syscalls.h>
> +#include <linux/utime.h>
>
> static __initdata char *message;
> static void __init error(char *x)
> @@ -72,6 +73,38 @@ static void __init free_hash(void)
> }
> }
>
> +static __initdata LIST_HEAD(dir_list);
> +struct dir_entry {
> + struct list_head list;
> + char *name;
> + struct utimbuf mtime;
> +};
> +
> +static void __init dir_add(const char *name, struct utimbuf mtime)
> +{
> + struct dir_entry *de = kmalloc(sizeof(struct dir_entry), GFP_KERNEL);
> + if (!de)
> + panic("can't allocate dir_entry buffer");
> + INIT_LIST_HEAD(&de->list);
> + de->name = kstrdup(name, GFP_KERNEL);
> + de->mtime = mtime;
> + list_add(&de->list, &dir_list);
> +}
> +
> +static void __init dir_utime(void)
> +{
> + struct list_head *e, *tmp;
> + list_for_each_safe(e, tmp, &dir_list) {
> + struct dir_entry *de = list_entry(e, struct dir_entry, list);
> + list_del(e);
> + sys_utime(de->name, &de->mtime);
gargh. Why does this work? It's normally a big fail to pass a kernel
address into a system call. I guess we're running under KERNEL_DS here
and getname() and strncpy_from_user() did the right thing.
On what CPU architecture was this tested?
Wouldn't it be simpler to put a timespec into struct dir_entry then go
direct to do_utimes() here?
> + kfree(de->name);
> + kfree(de);
> + }
> +}
> +
> +static __initdata struct utimbuf mtime;
> +
> /* cpio header parsing */
>
> static __initdata unsigned long ino, major, minor, nlink;
> @@ -97,6 +130,7 @@ static void __init parse_header(char *s)
> uid = parsed[2];
> gid = parsed[3];
> nlink = parsed[4];
> + mtime.actime = mtime.modtime = parsed[5];
> body_len = parsed[6];
> major = parsed[7];
> minor = parsed[8];
> @@ -130,6 +164,7 @@ static inline void __init eat(unsigned n)
> count -= n;
> }
>
> +static __initdata char *vcollected;
> static __initdata char *collected;
> static __initdata int remains;
> static __initdata char *collect;
> @@ -271,6 +306,7 @@ static int __init do_name(void)
> if (wfd >= 0) {
> sys_fchown(wfd, uid, gid);
> sys_fchmod(wfd, mode);
> + vcollected = kstrdup(collected, GFP_KERNEL);
> state = CopyFile;
> }
> }
> @@ -278,12 +314,14 @@ static int __init do_name(void)
> sys_mkdir(collected, mode);
> sys_chown(collected, uid, gid);
> sys_chmod(collected, mode);
> + dir_add(collected, mtime);
> } else if (S_ISBLK(mode) || S_ISCHR(mode) ||
> S_ISFIFO(mode) || S_ISSOCK(mode)) {
> if (maybe_link() == 0) {
> sys_mknod(collected, mode, rdev);
> sys_chown(collected, uid, gid);
> sys_chmod(collected, mode);
> + sys_utime(collected, &mtime);
> }
> }
> return 0;
> @@ -294,6 +332,8 @@ static int __init do_copy(void)
> if (count >= body_len) {
> sys_write(wfd, victim, body_len);
> sys_close(wfd);
> + sys_utime(vcollected, &mtime);
and here?
> + kfree(vcollected);
> eat(body_len);
> state = SkipIt;
> return 0;
> @@ -305,12 +345,26 @@ static int __init do_copy(void)
> }
> }
>
> +static long __init do_lutime(char __user *filename,
> + struct utimbuf __user *times)
> +{
> + struct timespec t[2];
> +
> + t[0].tv_sec = times->actime;
> + t[0].tv_nsec = 0;
> + t[1].tv_sec = times->modtime;
> + t[1].tv_nsec = 0;
> +
> + return do_utimes(AT_FDCWD, filename, t, AT_SYMLINK_NOFOLLOW);
> +}
> +
> static int __init do_symlink(void)
> {
> collected[N_ALIGN(name_len) + body_len] = '\0';
> clean_path(collected, 0);
> sys_symlink(collected + N_ALIGN(name_len), collected);
> sys_lchown(collected, uid, gid);
> + do_lutime(collected, &mtime);
> state = SkipIt;
> next_state = Reset;
> return 0;
> @@ -466,6 +520,7 @@ static char * __init unpack_to_rootfs(char *buf, unsigned len, int check_only)
> buf += inptr;
> len -= inptr;
> }
> + dir_utime();
Perhaps this is the simplest implementation - I didn't check the fine
details. What's your thinking here?
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