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On Wed, Feb 11, 2015 at 10:15:30PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> Add a basic implementation of RENAME_WHITEOUT to the XFS rename
> code. The implementation options considered are documented in the
> code comments; the method chose was "copy ext4" because we are then
> bug-for-bug compatible with the implementation done by the
> overlayfs developers.
>
> I have a hacky renameat2 test for whiteouts copied from the existing
> renameat2 tests in xfstests, and this code behaves the same as ext4
> in that rename test. I haven't done any testing with overlayfs, so
> who knows whether that explodes or not.
>
> The rename code is getting pretty spaghetti now - I'll end up
> spliting this patching whiteout support and cleanup, and I'll set
> what possible cleanups I can make that will help make the code a
> little more understandable....
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_inode.c | 261 +++++++++++++++++++++++++++++++++++++++++------------
> fs/xfs/xfs_iops.c | 2 +-
> 2 files changed, 205 insertions(+), 58 deletions(-)
>
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index bf2d2c7..eef5db7 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2683,17 +2683,20 @@ xfs_remove(
> */
> STATIC void
> xfs_sort_for_rename(
> - xfs_inode_t *dp1, /* in: old (source) directory inode */
> - xfs_inode_t *dp2, /* in: new (target) directory inode */
> - xfs_inode_t *ip1, /* in: inode of old entry */
> - xfs_inode_t *ip2, /* in: inode of new entry, if it
> - already exists, NULL otherwise. */
> - xfs_inode_t **i_tab,/* out: array of inode returned, sorted */
> - int *num_inodes) /* out: number of inodes in array */
> + struct xfs_inode *dp1, /* in: old (source) directory inode */
> + struct xfs_inode *dp2, /* in: new (target) directory inode */
> + struct xfs_inode *ip1, /* in: inode of old entry */
> + struct xfs_inode *ip2, /* in: inode of new entry */
> + struct xfs_inode *wino, /* in: whiteout inode */
> + struct xfs_inode **i_tab,/* out: sorted array of inodes */
> + int *num_inodes) /* out: inodes in array */
> {
> xfs_inode_t *temp;
> int i, j;
>
> + ASSERT(*num_inodes == 5);
> + memset(i_tab, 0, *num_inodes * sizeof(struct xfs_inode *));
> +
> /*
> * i_tab contains a list of pointers to inodes. We initialize
> * the table here & we'll sort it. We will then use it to
> @@ -2701,20 +2704,19 @@ xfs_sort_for_rename(
> *
> * Note that the table may contain duplicates. e.g., dp1 == dp2.
> */
> - i_tab[0] = dp1;
> - i_tab[1] = dp2;
> - i_tab[2] = ip1;
> - if (ip2) {
> - *num_inodes = 4;
> - i_tab[3] = ip2;
> - } else {
> - *num_inodes = 3;
> - i_tab[3] = NULL;
> - }
> + i = 0;
> + i_tab[i++] = dp1;
> + i_tab[i++] = dp2;
> + i_tab[i++] = ip1;
> + if (ip2)
> + i_tab[i++] = ip2;
> + if (wino)
> + i_tab[i++] = wino;
> + *num_inodes = i;
>
> /*
> * Sort the elements via bubble sort. (Remember, there are at
> - * most 4 elements to sort, so this is adequate.)
> + * most 5 elements to sort, so this is adequate.)
> */
> for (i = 0; i < *num_inodes; i++) {
> for (j = 1; j < *num_inodes; j++) {
> @@ -2846,6 +2848,101 @@ out:
> }
>
> /*
> + * RENAME_WHITEOUT support.
> + *
> + * Whiteouts are used by overlayfs - it has a convention that a whiteout is a
> + * character device inode with a major:minor of 0:0. Somebody has to be in an
> + * altered state of mind to think this up, so whiteout inodes from this point at
> + * called "wino"s.
> + *
> + * Now, because it's not documented anywhere, here's what RENAME_WHITEOUT does
> + * on ext4:
> +
> +# echo bar > /mnt/scratch/bar
> +# ls -l /mnt/scratch
> +total 24
> +-rw-r--r-- 1 root root 4 Feb 11 20:22 bar
> +-rw-r--r-- 1 root root 4 Feb 11 20:22 foo
> +drwx------ 2 root root 16384 Feb 11 20:18 lost+found
> +# src/renameat2 -w /mnt/scratch/foo /mnt/scratch/bar
> +# ls -l /mnt/scratch
> +total 20
> +-rw-r--r-- 1 root root 4 Feb 11 20:22 bar
> +c--------- 1 root root 0, 0 Feb 11 20:23 foo
> +drwx------ 2 root root 16384 Feb 11 20:18 lost+found
> +# cat /mnt/scratch/bar
> +foo
> +#
> +
> + * In XFS rename terms, the operation that has been done is that source (foo)
> + * has been moved to the target (bar), which is like a nomal rename operation,
> + * but rather than the source being removed, it have been replaced with a wino.
> + *
> + * We can't allocate winos within the rename transaction due to allocation
> + * being a multi-commit transaction, and rename needs to be a single, atomic
> + * commit. Hence we have several options here, form most efficient to least
> + * efficient:
> + *
> + * - use DT_WHT in the target dirent and do no wino allocation.
> + * The main issue with this approach is that we need hooks in
> + * lookup to create a virtual chardev inode to present to userspace
> + * and in places where we might need to modify the dirent e.g. unlink.
> + * Overlayfs also needs to be taught about DT_WHT. Most invasive change,
> + * lowest overhead.
> + *
> + * - create a special wino in the root directory (e.g. a ".wino" dirent and
> + * then hardlink every new whiteout to it. This means we only need to
> + * create a single wino, and rename simply creates a hardlink to it. We
> + * can use DT_WHT for these, though using DT_CHR means we won't have to
> + * modify overlayfs, nor anything in userspace. Downside is we have to
> + * look up the wino up on every operation and create it if it doesn't
> + * exist.
> + *
> + * - copy ext4: create a special whiteout chardev inode for every whiteout.
> + * This is more complex than the above options because of the lack of
> + * atomicity between inode creation and the rename operation, requiring
> + * us to create a tmpfile inode and then linking it into the directory
> + * structure during the rename. At least with a tmpfile inode crashes
> + * between the create and rename doesn't leave unreferenced inodes or
> + * directory pollution around.
> + *
> + * By far the simplest thing to do is copy ext4. It's also the most
> + * inefficient way of supporting whiteouts, but as an initial implementation we
> + * can simply reuse existing functions and add a small amount of extra code the
> + * the rename operation to handle the *fifth* inode in the transaction.
> + *
> + * Hence that is what is implemented first. When we have time or need we can
> + * come back and implement one of the more efficient whiteout methods, but it's
> + * not necessary for the first implementation.
> + */
> +
> +/*
> + * xfs_rename_get_wino()
> + *
> + * Return a referenced, unlinked, unlocked inode that that can be used as a
> + * whiteout in a rename transaction.
> + */
> +static int
> +xfs_rename_get_wino(
> + struct xfs_inode *dp,
> + struct xfs_inode **wino)
> +{
> + struct xfs_inode *tmpfile;
> + int error;
> +
> + error = xfs_create_tmpfile(dp, NULL, S_IFCHR | WHITEOUT_MODE, &tmpfile);
> + if (error)
> + return error;
> +
> + /* Satisfy xfs_bumplink that this is a real tmpfile */
> + xfs_finish_inode_setup(tmpfile);
> + VFS_I(tmpfile)->i_state |= I_LINKABLE;
> +
> + *wino = tmpfile;
> + return 0;
> +}
> +
> +/*
> * xfs_rename
> */
> int
> @@ -2867,40 +2964,52 @@ xfs_rename(
> xfs_fsblock_t first_block;
> int cancel_flags;
> int committed;
> - xfs_inode_t *inodes[4];
> + xfs_inode_t *inodes[5];
> + int num_inodes = 5;
> int spaceres;
> - int num_inodes;
> + struct xfs_inode *wino = NULL;
>
> trace_xfs_rename(src_dp, target_dp, src_name, target_name);
>
> + /*
> + * If we are doing a whiteout operation, get us the wino we will be
> + * placing at the target.
> + */
> + if (flags & RENAME_WHITEOUT) {
> + ASSERT(!(flags & (RENAME_NOREPLACE | RENAME_EXCHANGE)));
> + error = xfs_rename_get_wino(target_dp, &wino);
> + if (error)
> + return error;
> +
> + /* setup target dirent info as whiteout */
> + src_name->type = XFS_DIR3_FT_CHRDEV;
> + }
> +
> new_parent = (src_dp != target_dp);
> src_is_directory = S_ISDIR(src_ip->i_d.di_mode);
>
> - xfs_sort_for_rename(src_dp, target_dp, src_ip, target_ip,
> + xfs_sort_for_rename(src_dp, target_dp, src_ip, target_ip, wino,
> inodes, &num_inodes);
>
> + cancel_flags = 0;
> xfs_bmap_init(&free_list, &first_block);
> tp = xfs_trans_alloc(mp, XFS_TRANS_RENAME);
> - cancel_flags = XFS_TRANS_RELEASE_LOG_RES;
> spaceres = XFS_RENAME_SPACE_RES(mp, target_name->len);
> error = xfs_trans_reserve(tp, &M_RES(mp)->tr_rename, spaceres, 0);
> if (error == -ENOSPC) {
> spaceres = 0;
> error = xfs_trans_reserve(tp, &M_RES(mp)->tr_rename, 0, 0);
> }
> - if (error) {
> - xfs_trans_cancel(tp, 0);
> - goto std_return;
> - }
> + if (error)
> + goto error_trans_cancel;
> + cancel_flags = XFS_TRANS_RELEASE_LOG_RES;
>
> /*
> * Attach the dquots to the inodes
> */
> error = xfs_qm_vop_rename_dqattach(inodes);
> - if (error) {
> - xfs_trans_cancel(tp, cancel_flags);
> - goto std_return;
> - }
> + if (error)
> + goto error_trans_cancel;
>
> /*
> * Lock all the participating inodes. Depending upon whether
> @@ -2921,6 +3030,8 @@ xfs_rename(
> xfs_trans_ijoin(tp, src_ip, XFS_ILOCK_EXCL);
> if (target_ip)
> xfs_trans_ijoin(tp, target_ip, XFS_ILOCK_EXCL);
> + if (wino)
> + xfs_trans_ijoin(tp, wino, XFS_ILOCK_EXCL);
>
> /*
> * If we are using project inheritance, we only allow renames
> @@ -2930,18 +3041,19 @@ xfs_rename(
> if (unlikely((target_dp->i_d.di_flags & XFS_DIFLAG_PROJINHERIT) &&
> (xfs_get_projid(target_dp) != xfs_get_projid(src_ip)))) {
> error = -EXDEV;
> - goto error_return;
> + goto error_trans_cancel;
> }
>
> /*
> * Handle RENAME_EXCHANGE flags
> */
> if (flags & RENAME_EXCHANGE) {
> + ASSERT(!wino);
> error = xfs_cross_rename(tp, src_dp, src_name, src_ip,
> target_dp, target_name, target_ip,
> &free_list, &first_block, spaceres);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
> goto finish_rename;
> }
>
> @@ -2956,7 +3068,7 @@ xfs_rename(
> if (!spaceres) {
> error = xfs_dir_canenter(tp, target_dp, target_name);
> if (error)
> - goto error_return;
> + goto error_trans_cancel;
> }
> /*
> * If target does not exist and the rename crosses
> @@ -2967,9 +3079,9 @@ xfs_rename(
> src_ip->i_ino, &first_block,
> &free_list, spaceres);
> if (error == -ENOSPC)
> - goto error_return;
> + goto error_trans_cancel;
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
>
> xfs_trans_ichgtime(tp, target_dp,
> XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
> @@ -2977,7 +3089,7 @@ xfs_rename(
> if (new_parent && src_is_directory) {
> error = xfs_bumplink(tp, target_dp);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
> }
> } else { /* target_ip != NULL */
> /*
> @@ -2992,7 +3104,7 @@ xfs_rename(
> if (!(xfs_dir_isempty(target_ip)) ||
> (target_ip->i_d.di_nlink > 2)) {
> error = -EEXIST;
> - goto error_return;
> + goto error_trans_cancel;
> }
> }
>
> @@ -3009,7 +3121,7 @@ xfs_rename(
> src_ip->i_ino,
> &first_block, &free_list, spaceres);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
>
> xfs_trans_ichgtime(tp, target_dp,
> XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
> @@ -3020,7 +3132,7 @@ xfs_rename(
> */
> error = xfs_droplink(tp, target_ip);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
>
> if (src_is_directory) {
> /*
> @@ -3028,9 +3140,9 @@ xfs_rename(
> */
> error = xfs_droplink(tp, target_ip);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
> }
> - } /* target_ip != NULL */
> + }
>
> /*
> * Remove the source.
> @@ -3045,7 +3157,7 @@ xfs_rename(
> &first_block, &free_list, spaceres);
> ASSERT(error != -EEXIST);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
> }
>
> /*
> @@ -3071,13 +3183,21 @@ xfs_rename(
> */
> error = xfs_droplink(tp, src_dp);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
> }
>
> - error = xfs_dir_removename(tp, src_dp, src_name, src_ip->i_ino,
> + /*
> + * On a whiteout, we only update the source dirent with the wino,
> + * otherwise we are removing it.
> + */
> + if (wino) {
> + error = xfs_dir_replace(tp, src_dp, src_name, wino->i_ino,
> + &first_block, &free_list, spaceres);
> + } else
> + error = xfs_dir_removename(tp, src_dp, src_name, src_ip->i_ino,
> &first_block, &free_list, spaceres);
> if (error)
> - goto abort_return;
> + goto error_trans_abort;
>
> xfs_trans_ichgtime(tp, src_dp, XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
> xfs_trans_log_inode(tp, src_dp, XFS_ILOG_CORE);
> @@ -3090,31 +3210,58 @@ finish_rename:
> * rename transaction goes to disk before returning to
> * the user.
> */
> - if (mp->m_flags & (XFS_MOUNT_WSYNC|XFS_MOUNT_DIRSYNC)) {
> + if (mp->m_flags & (XFS_MOUNT_WSYNC|XFS_MOUNT_DIRSYNC))
> xfs_trans_set_sync(tp);
> - }
>
> error = xfs_bmap_finish(&tp, &free_list, &committed);
> - if (error) {
> - xfs_bmap_cancel(&free_list);
> - xfs_trans_cancel(tp, (XFS_TRANS_RELEASE_LOG_RES |
> - XFS_TRANS_ABORT));
> - goto std_return;
> + if (error)
> + goto error_trans_abort;
> +
> + /*
> + * Last thing we do is bump the link count on the wino. This means that
> + * failures all the way up to this point leave the wino on the unlinked
> + * list and so cleanup is a simple matter of dropping the remaining
> + * reference to it. If we fail here after bumping the link count, we're
> + * shutting down the filesystem so we'll never see the intermediate
> + * state on disk.
> + */
> + if (wino) {
> + ASSERT(wino->i_d.di_nlink == 0);
> + error = xfs_bumplink(tp, wino);
> + if (error)
> + goto error_trans_abort;
> + error = xfs_iunlink_remove(tp, wino);
> + if (error)
> + goto error_trans_abort;
> + xfs_trans_log_inode(tp, wino, XFS_ILOG_CORE);
> +
> + /*
> + * now we have a real link, clear the "I'm a tmpfile" state
> + * flag from the inode so it doesn't accidentally get misused in
> + * future.
> + */
> + VFS_I(wino)->i_state &= ~I_LINKABLE;
> }
>
> /*
> * trans_commit will unlock src_ip, target_ip & decrement
> * the vnode references.
> */
> - return xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
> + error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
> +out_release_wino:
> + if (wino)
> + IRELE(wino);
> + return error;
>
> - abort_return:
> +
> +error_trans_abort:
> cancel_flags |= XFS_TRANS_ABORT;
> - error_return:
> xfs_bmap_cancel(&free_list);
> +error_trans_cancel:
> xfs_trans_cancel(tp, cancel_flags);
> - std_return:
> - return error;
> +
> + /* Dropping the last reference on a tmpfile does the cleanup for us! */
> + goto out_release_wino;
> }
>
> STATIC int
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 6a77ea9..d4442d1 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -393,7 +393,7 @@ xfs_vn_rename(
> struct xfs_name oname;
> struct xfs_name nname;
>
> - if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
> + if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE | RENAME_WHITEOUT))
> return -EINVAL;
>
> /* if we are exchanging files, we need to set i_mode of both files */
> --
> 2.0.0
>
> _______________________________________________
> xfs mailing list
> xfs@xxxxxxxxxxx
> http://oss.sgi.com/mailman/listinfo/xfs
>
--
Dave Chinner
david@xxxxxxxxxxxxx
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