[PATCH]jffs2:bugfix for should not appeared directory hard link
liu.song11 at zte.com.cn
liu.song11 at zte.com.cn
Wed Mar 11 20:05:34 PDT 2015
Hi David，
Apologies for the delay of this reply that caused by taken holiday of the Spring Festival.
I have tested your codes and found it can work very well. I think this solution is very
subtle, simple and reasonable, I really like this solution, thanks a lot.
Best Regards
David Woodhouse <dwmw2 at infradead.org> wrote on 2015-02-13 19:28:01:
> From: David Woodhouse <dwmw2 at infradead.org>
> To: liu.song11 at zte.com.cn,
> Cc: cui.yunfeng at zte.com.cn, deng.chao1 at zte.com.cn, jiang.xuexin at zte.com.cn, linux-mtd at lists.infradead.org, wang.bo116 at zte.com.cn
> Date: 2015-02-13 19:28
> Subject: Re: [PATCH]jffs2:bugfix for should not appeared directory hard link
>
> On Fri, 2015-02-13 at 10:13 +0000, David Woodhouse wrote:
> >
> > If <ino#71> is somehow ending up linked as /mnt/foo again when it should
> > have been unlinked, *that* is the problem we need to be looking at. The
> > zombie *children* of <ino#71> are just a symptom of its reincarnation.
>
> Ah, I think I understand a little better.
>
> At the time the problem happens, it's too *early* in the scan/build
> process. We don't yet *know* that ino#71 is dead, because we haven't yet
> scanned the whole flash looking for dirents that might point to it.
>
> In the problematic case, the directory SW1<#2> is first discovered when
> we see its dirent from the *dead* directory <#71>, and we fill in
> ic<2>->pino_nlink = 71.
>
> And then *later* we find the *real* dirent which links SW1<#2> from the
> root directory, and we hit that 'appears to be a hard link' message in
> jffs2_build_inode_pass1().
>
> The problem really comes when we *later* kill ino#71 because we realise
> it doesn't have any valid dirents keeping it alive, and we *also* kill
> all its children. Some of which weren't *really* supposed to be its
> children :)
>
> If we happened to hit the real dirent for SW1<#2> *first*, and the
> dirent linking it from <#71> *later*, then we'd be OK.
>
> This is all because of the NFS export support, which means we have to
> know the parent inode# for directories. If we were still storing nlink
> for directories as we do for plain files, we could fix this fairly
> easily.
>
> Your approach is to fix the garbage collection, to ensure that the old
> deletion dirents "unlinking" SW1<#2> from the dead <ino#71> aren't
> actually allowed to expire until all previous *positive* dirents linking
> it into that dead parent directory have also expired ― much like we
> already do for garbage collection of deletion dirents in a live
> directory.
>
> That makes sense, but I'm not sure I like it very much. It's complex,
> and it really does violate my sense of decency a little ― if <ino#71> is
> dead when it should *stay* dead, and not return to bother us.
>
> I'll see if I can come up with a simpler solution purely within the scan
> code. Can you test this, please?
>
> diff --git a/fs/jffs2/build.c b/fs/jffs2/build.c
> index a3750f9..f5a9b0e 100644
> --- a/fs/jffs2/build.c
> +++ b/fs/jffs2/build.c
> @@ -49,7 +49,8 @@ next_inode(int *i, struct jffs2_inode_cache *ic, struct jffs2_sb_info *c)
>
>
> static void jffs2_build_inode_pass1(struct jffs2_sb_info *c,
> - struct jffs2_inode_cache *ic)
> + struct jffs2_inode_cache *ic,
> + int *dir_hardlinks)
> {
> struct jffs2_full_dirent *fd;
>
> @@ -71,16 +72,16 @@ static void jffs2_build_inode_pass1(struct jffs2_sb_info *c,
> continue;
> }
>
> + /* From this point, fd->raw is no longer used so we can set fd->ic */
> + fd->ic = child_ic;
> + child_ic->pino_nlink++;
> + /* If we appear (at this stage) to have hard-linked directories,
> + * set a flag to trigger a scan later */
> if (fd->type == DT_DIR) {
> - if (child_ic->pino_nlink) {
> - JFFS2_ERROR("child dir \"%s\" (ino #%u) of dir ino #%u appears to be a hard link\n",
> - fd->name, fd->ino, ic->ino);
> - /* TODO: What do we do about it? */
> - } else {
> - child_ic->pino_nlink = ic->ino;
> - }
> - } else
> - child_ic->pino_nlink++;
> + child_ic->flags |= INO_FLAGS_IS_DIR;
> + if (child_ic->pino_nlink > 1)
> + *dir_hardlinks = 1;
> + }
>
> dbg_fsbuild("increased nlink for child \"%s\" (ino #%u)\n", fd->name, fd->ino);
> /* Can't free scan_dents so far. We might need them in pass 2 */
> @@ -94,8 +95,7 @@ static void jffs2_build_inode_pass1(struct jffs2_sb_info *c,
> */
> static int jffs2_build_filesystem(struct jffs2_sb_info *c)
> {
> - int ret;
> - int i;
> + int ret, i, dir_hardlinks = 0;
> struct jffs2_inode_cache *ic;
> struct jffs2_full_dirent *fd;
> struct jffs2_full_dirent *dead_fds = NULL;
> @@ -119,7 +119,7 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
> /* Now scan the directory tree, increasing nlink according to every dirent found. */
> for_each_inode(i, c, ic) {
> if (ic->scan_dents) {
> - jffs2_build_inode_pass1(c, ic);
> + jffs2_build_inode_pass1(c, ic, &dir_hardlinks);
> cond_resched();
> }
> }
> @@ -155,6 +155,20 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
> }
>
> dbg_fsbuild("pass 2a complete\n");
> +
> + if (dir_hardlinks) {
> + /* If we detected directory hardlinks earlier, *hopefully*
> + * they are gone now because some of the links were from
> + * dead directories which still had some old dirents lying
> + * around and not yet garbage-collected, but which have
> + * been discarded above. So clear the pino_nlink field
> + * in each directory, so that the final scan below can
> + * print appropriate warnings. */
> + for_each_inode(i, c, ic) {
> + if (ic->flags & INO_FLAGS_IS_DIR)
> + ic->pino_nlink = 0;
> + }
> + }
> dbg_fsbuild("freeing temporary data structures\n");
>
> /* Finally, we can scan again and free the dirent structs */
> @@ -162,6 +176,18 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
> while(ic->scan_dents) {
> fd = ic->scan_dents;
> ic->scan_dents = fd->next;
> + /* We do use the pino_nlink field to count nlink of
> + * directories during fs build, so set it to the
> + * parent ino# now. Now that there's hopefully only
> + * one. */
> + if (fd->type == DT_DIR) {
> + if (dir_hardlinks && fd->ic->pino_nlink) {
> + JFFS2_ERROR("child dir \"%s\" (ino #%u) of dir ino #%u is also hard linked from dir ino #%u\n",
> + fd->name, fd->ino, ic->ino, fd->ic->pino_nlink);
> + /* Should we unlink it from its previous parent? */
> + }
> + fd->ic->pino_nlink = ic->ino;
> + }
> jffs2_free_full_dirent(fd);
> }
> ic->scan_dents = NULL;
> @@ -240,11 +266,7 @@ static void jffs2_build_remove_unlinked_inode(struct jffs2_sb_info *c,
>
> /* Reduce nlink of the child. If it's now zero, stick it on the
> dead_fds list to be cleaned up later. Else just free the fd */
> -
> - if (fd->type == DT_DIR)
> - child_ic->pino_nlink = 0;
> - else
> - child_ic->pino_nlink--;
> + child_ic->pino_nlink--;
>
> if (!child_ic->pino_nlink) {
> dbg_fsbuild("inode #%u (\"%s\") now has no links; adding to dead_fds list.\n",
> diff --git a/fs/jffs2/nodelist.h b/fs/jffs2/nodelist.h
> index fa35ff7..0637271 100644
> --- a/fs/jffs2/nodelist.h
> +++ b/fs/jffs2/nodelist.h
> @@ -194,6 +194,7 @@ struct jffs2_inode_cache {
> #define INO_STATE_CLEARING 6 /* In clear_inode() */
>
> #define INO_FLAGS_XATTR_CHECKED 0x01 /* has no duplicate xattr_ref */
> +#define INO_FLAGS_IS_DIR 0x02 /* is a directory */
>
> #define RAWNODE_CLASS_INODE_CACHE 0
> #define RAWNODE_CLASS_XATTR_DATUM 1
> @@ -249,7 +250,10 @@ struct jffs2_readinode_info
>
> struct jffs2_full_dirent
> {
> - struct jffs2_raw_node_ref *raw;
> + union {
> + struct jffs2_raw_node_ref *raw;
> + struct jffs2_inode_cache *ic; /* Just during part of build */
> + };
> struct jffs2_full_dirent *next;
> uint32_t version;
> uint32_t ino; /* == zero for unlink */
>
>
> --
> dwmw2
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