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Message-ID: <20080903224130.GA16630@curtisfong.org>
Date: Wed, 3 Sep 2008 15:41:31 -0700
From: Nye Liu <nyet@...t.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, nyet@....com
Subject: Re: [PATCH] INITRAMFS: Add option to preserve mtime from INITRAMFS
cpio images
On Wed, Sep 03, 2008 at 03:22:31PM -0700, Andrew Morton wrote:
> On Wed, 3 Sep 2008 13:29:38 -0700
> > 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.
Possibly, i was not aware of that limitation :( I'll look into it
> On what CPU architecture was this tested?
ppc and powerpc
> Wouldn't it be simpler to put a timespec into struct dir_entry then go
> direct to do_utimes() here?
No, if i understand your question correctly. I have to do the mtime
modifications in two passes (see last comment below)
>
> > + 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?
see below regarding two passes.
> > + 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?
>
The main problem is that i need to save off the entire list for later
processing of the directory mtimes... if i process the directory mtimes
in the same pass as the file/link mtimes, touching the directory inode
when creating/modifying the file/links updates the directory mtime, and
overwrites whatever mtime i set the directory to when i created it.
The only solution is to do a two pass, which is why the list is
necessary. If there is a better way, i did not find it :(
It could be that i misunderstood your question though :)
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