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Commit 766702ef authored by Alexander Block's avatar Alexander Block Committed by Chris Mason
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Btrfs: add/fix comments/documentation for send/receive 

As the subject already said, add/fix comments.
Signed-off-by: default avatarAlexander Block <ablock84@googlemail.com>
parent e479d9bb
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Showing with 134 additions and 6 deletions
fs/btrfs/send.c
View file @ 766702ef
......@@ -1067,6 +1067,7 @@ static int __clone_root_cmp_sort(const void *e1, const void *e2)
/*
* Called for every backref that is found for the current extent.
* Results are collected in sctx->clone_roots->ino/offset/found_refs
*/
static int __iterate_backrefs(u64 ino, u64 offset, u64 root, void *ctx_)
{
......@@ -1090,7 +1091,7 @@ static int __iterate_backrefs(u64 ino, u64 offset, u64 root, void *ctx_)
}
/*
* There are inodes that have extents that lie behind it's i_size. Don't
* There are inodes that have extents that lie behind its i_size. Don't
* accept clones from these extents.
*/
ret = get_inode_info(found->root, ino, &i_size, NULL, NULL, NULL, NULL,
......@@ -1137,6 +1138,12 @@ static int __iterate_backrefs(u64 ino, u64 offset, u64 root, void *ctx_)
}
/*
* Given an inode, offset and extent item, it finds a good clone for a clone
* instruction. Returns -ENOENT when none could be found. The function makes
* sure that the returned clone is usable at the point where sending is at the
* moment. This means, that no clones are accepted which lie behind the current
* inode+offset.
*
* path must point to the extent item when called.
*/
static int find_extent_clone(struct send_ctx *sctx,
......@@ -1529,6 +1536,10 @@ static int lookup_dir_item_inode(struct btrfs_root *root,
return ret;
}
/*
* Looks up the first btrfs_inode_ref of a given ino. It returns the parent dir,
* generation of the parent dir and the name of the dir entry.
*/
static int get_first_ref(struct send_ctx *sctx,
struct btrfs_root *root, u64 ino,
u64 *dir, u64 *dir_gen, struct fs_path *name)
......@@ -1615,6 +1626,16 @@ static int is_first_ref(struct send_ctx *sctx,
return ret;
}
/*
* Used by process_recorded_refs to determine if a new ref would overwrite an
* already existing ref. In case it detects an overwrite, it returns the
* inode/gen in who_ino/who_gen.
* When an overwrite is detected, process_recorded_refs does proper orphanizing
* to make sure later references to the overwritten inode are possible.
* Orphanizing is however only required for the first ref of an inode.
* process_recorded_refs does an additional is_first_ref check to see if
* orphanizing is really required.
*/
static int will_overwrite_ref(struct send_ctx *sctx, u64 dir, u64 dir_gen,
const char *name, int name_len,
u64 *who_ino, u64 *who_gen)
......@@ -1639,6 +1660,11 @@ static int will_overwrite_ref(struct send_ctx *sctx, u64 dir, u64 dir_gen,
goto out;
}
/*
* Check if the overwritten ref was already processed. If yes, the ref
* was already unlinked/moved, so we can safely assume that we will not
* overwrite anything at this point in time.
*/
if (other_inode > sctx->send_progress) {
ret = get_inode_info(sctx->parent_root, other_inode, NULL,
who_gen, NULL, NULL, NULL, NULL);
......@@ -1655,6 +1681,13 @@ static int will_overwrite_ref(struct send_ctx *sctx, u64 dir, u64 dir_gen,
return ret;
}
/*
* Checks if the ref was overwritten by an already processed inode. This is
* used by __get_cur_name_and_parent to find out if the ref was orphanized and
* thus the orphan name needs be used.
* process_recorded_refs also uses it to avoid unlinking of refs that were
* overwritten.
*/
static int did_overwrite_ref(struct send_ctx *sctx,
u64 dir, u64 dir_gen,
u64 ino, u64 ino_gen,
......@@ -1703,6 +1736,11 @@ static int did_overwrite_ref(struct send_ctx *sctx,
return ret;
}
/*
* Same as did_overwrite_ref, but also checks if it is the first ref of an inode
* that got overwritten. This is used by process_recorded_refs to determine
* if it has to use the path as returned by get_cur_path or the orphan name.
*/
static int did_overwrite_first_ref(struct send_ctx *sctx, u64 ino, u64 gen)
{
int ret = 0;
......@@ -1731,6 +1769,11 @@ static int did_overwrite_first_ref(struct send_ctx *sctx, u64 ino, u64 gen)
return ret;
}
/*
* Insert a name cache entry. On 32bit kernels the radix tree index is 32bit,
* so we need to do some special handling in case we have clashes. This function
* takes care of this with the help of name_cache_entry::radix_list.
*/
static int name_cache_insert(struct send_ctx *sctx,
struct name_cache_entry *nce)
{
......@@ -1792,12 +1835,19 @@ static struct name_cache_entry *name_cache_search(struct send_ctx *sctx,
return NULL;
}
/*
* Removes the entry from the list and adds it back to the end. This marks the
* entry as recently used so that name_cache_clean_unused does not remove it.
*/
static void name_cache_used(struct send_ctx *sctx, struct name_cache_entry *nce)
{
list_del(&nce->list);
list_add_tail(&nce->list, &sctx->name_cache_list);
}
/*
* Remove some entries from the beginning of name_cache_list.
*/
static void name_cache_clean_unused(struct send_ctx *sctx)
{
struct name_cache_entry *nce;
......@@ -1824,6 +1874,14 @@ static void name_cache_free(struct send_ctx *sctx)
}
}
/*
* Used by get_cur_path for each ref up to the root.
* Returns 0 if it succeeded.
* Returns 1 if the inode is not existent or got overwritten. In that case, the
* name is an orphan name. This instructs get_cur_path to stop iterating. If 1
* is returned, parent_ino/parent_gen are not guaranteed to be valid.
* Returns <0 in case of error.
*/
static int __get_cur_name_and_parent(struct send_ctx *sctx,
u64 ino, u64 gen,
u64 *parent_ino,
......@@ -1835,6 +1893,11 @@ static int __get_cur_name_and_parent(struct send_ctx *sctx,
struct btrfs_path *path = NULL;
struct name_cache_entry *nce = NULL;
/*
* First check if we already did a call to this function with the same
* ino/gen. If yes, check if the cache entry is still up-to-date. If yes
* return the cached result.
*/
nce = name_cache_search(sctx, ino, gen);
if (nce) {
if (ino < sctx->send_progress && nce->need_later_update) {
......@@ -1857,6 +1920,11 @@ static int __get_cur_name_and_parent(struct send_ctx *sctx,
if (!path)
return -ENOMEM;
/*
* If the inode is not existent yet, add the orphan name and return 1.
* This should only happen for the parent dir that we determine in
* __record_new_ref
*/
ret = is_inode_existent(sctx, ino, gen);
if (ret < 0)
goto out;
......@@ -1869,6 +1937,10 @@ static int __get_cur_name_and_parent(struct send_ctx *sctx,
goto out_cache;
}
/*
* Depending on whether the inode was already processed or not, use
* send_root or parent_root for ref lookup.
*/
if (ino < sctx->send_progress)
ret = get_first_ref(sctx, sctx->send_root, ino,
parent_ino, parent_gen, dest);
......@@ -1878,6 +1950,10 @@ static int __get_cur_name_and_parent(struct send_ctx *sctx,
if (ret < 0)
goto out;
/*
* Check if the ref was overwritten by an inode's ref that was processed
* earlier. If yes, treat as orphan and return 1.
*/
ret = did_overwrite_ref(sctx, *parent_ino, *parent_gen, ino, gen,
dest->start, dest->end - dest->start);
if (ret < 0)
......@@ -1891,6 +1967,9 @@ static int __get_cur_name_and_parent(struct send_ctx *sctx,
}
out_cache:
/*
* Store the result of the lookup in the name cache.
*/
nce = kmalloc(sizeof(*nce) + fs_path_len(dest) + 1, GFP_NOFS);
if (!nce) {
ret = -ENOMEM;
......@@ -2278,7 +2357,7 @@ verbose_printk("btrfs: send_utimes %llu\n", ino);
btrfs_inode_mtime(ii));
TLV_PUT_BTRFS_TIMESPEC(sctx, BTRFS_SEND_A_CTIME, eb,
btrfs_inode_ctime(ii));
/* TODO otime? */
/* TODO Add otime support when the otime patches get into upstream */
ret = send_cmd(sctx);
......@@ -2520,7 +2599,7 @@ static void free_recorded_refs(struct send_ctx *sctx)
}
/*
* Renames/moves a file/dir to it's orphan name. Used when the first
* Renames/moves a file/dir to its orphan name. Used when the first
* ref of an unprocessed inode gets overwritten and for all non empty
* directories.
*/
......@@ -2840,7 +2919,9 @@ verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);
* If the inode is still orphan, unlink the orphan. This may
* happen when a previous inode did overwrite the first ref
* of this inode and no new refs were added for the current
* inode.
* inode. Unlinking does not mean that the inode is deleted in
* all cases. There may still be links to this inode in other
* places.
*/
if (is_orphan) {
ret = send_unlink(sctx, valid_path);
......@@ -2857,6 +2938,11 @@ verbose_printk("btrfs: process_recorded_refs %llu\n", sctx->cur_ino);
*/
ULIST_ITER_INIT(&uit);
while ((un = ulist_next(check_dirs, &uit))) {
/*
* In case we had refs into dirs that were not processed yet,
* we don't need to do the utime and rmdir logic for these dirs.
* The dir will be processed later.
*/
if (un->val > sctx->cur_ino)
continue;
......@@ -4048,7 +4134,17 @@ static int changed_inode(struct send_ctx *sctx,
sctx->cur_inode_mode = btrfs_inode_mode(
sctx->right_path->nodes[0], right_ii);
} else if (result == BTRFS_COMPARE_TREE_CHANGED) {
/*
* We need to do some special handling in case the inode was
* reported as changed with a changed generation number. This
* means that the original inode was deleted and new inode
* reused the same inum. So we have to treat the old inode as
* deleted and the new one as new.
*/
if (sctx->cur_inode_new_gen) {
/*
* First, process the inode as if it was deleted.
*/
sctx->cur_inode_gen = right_gen;
sctx->cur_inode_new = 0;
sctx->cur_inode_deleted = 1;
......@@ -4061,6 +4157,9 @@ static int changed_inode(struct send_ctx *sctx,
if (ret < 0)
goto out;
/*
* Now process the inode as if it was new.
*/
sctx->cur_inode_gen = left_gen;
sctx->cur_inode_new = 1;
sctx->cur_inode_deleted = 0;
......@@ -4080,6 +4179,11 @@ static int changed_inode(struct send_ctx *sctx,
* process_recorded_refs_if_needed in the new_gen case.
*/
sctx->send_progress = sctx->cur_ino + 1;
/*
* Now process all extents and xattrs of the inode as if
* they were all new.
*/
ret = process_all_extents(sctx);
if (ret < 0)
goto out;
......@@ -4102,6 +4206,16 @@ static int changed_inode(struct send_ctx *sctx,
return ret;
}
/*
* We have to process new refs before deleted refs, but compare_trees gives us
* the new and deleted refs mixed. To fix this, we record the new/deleted refs
* first and later process them in process_recorded_refs.
* For the cur_inode_new_gen case, we skip recording completely because
* changed_inode did already initiate processing of refs. The reason for this is
* that in this case, compare_tree actually compares the refs of 2 different
* inodes. To fix this, process_all_refs is used in changed_inode to handle all
* refs of the right tree as deleted and all refs of the left tree as new.
*/
static int changed_ref(struct send_ctx *sctx,
enum btrfs_compare_tree_result result)
{
......@@ -4122,6 +4236,11 @@ static int changed_ref(struct send_ctx *sctx,
return ret;
}
/*
* Process new/deleted/changed xattrs. We skip processing in the
* cur_inode_new_gen case because changed_inode did already initiate processing
* of xattrs. The reason is the same as in changed_ref
*/
static int changed_xattr(struct send_ctx *sctx,
enum btrfs_compare_tree_result result)
{
......@@ -4141,6 +4260,11 @@ static int changed_xattr(struct send_ctx *sctx,
return ret;
}
/*
* Process new/deleted/changed extents. We skip processing in the
* cur_inode_new_gen case because changed_inode did already initiate processing
* of extents. The reason is the same as in changed_ref
*/
static int changed_extent(struct send_ctx *sctx,
enum btrfs_compare_tree_result result)
{
......@@ -4157,7 +4281,10 @@ static int changed_extent(struct send_ctx *sctx,
return ret;
}
/*
* Updates compare related fields in sctx and simply forwards to the actual
* changed_xxx functions.
*/
static int changed_cb(struct btrfs_root *left_root,
struct btrfs_root *right_root,
struct btrfs_path *left_path,
......@@ -4229,7 +4356,8 @@ static int full_send_tree(struct send_ctx *sctx)
}
/*
* Make sure the tree has not changed
* Make sure the tree has not changed after re-joining. We detect this
* by comparing start_ctransid and ctransid. They should always match.
*/
spin_lock(&send_root->root_times_lock);
ctransid = btrfs_root_ctransid(&send_root->root_item);
......
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