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ovl: do not try to reconnect a disconnected origin dentry

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On lookup of non directory, we try to decode the origin file handle
stored in upper inode. The origin file handle is supposed to be decoded
to a disconnected non-dir dentry, which is fine, because we only need
the lower inode of a copy up origin.

However, if the origin file handle somehow turns out to be a directory
we pay the expensive cost of reconnecting the directory dentry, only to
get a mismatch file type and drop the dentry.

Optimize this case by explicitly opting out of reconnecting the dentry.
Opting-out of reconnect is done by passing a NULL acceptable callback
to exportfs_decode_fh().

While the case described above is a strange corner case that does not
really need to be optimized, the API added for this optimization will
be used by a following patch to optimize a more common case of decoding
an overlayfs file handle.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2018-03-09 15:51:02 +02:00 committed by Miklos Szeredi
parent 5b2cccd32c
commit 8a22efa15b
4 changed files with 23 additions and 11 deletions
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9
fs/exportfs/expfs.c
View File

@ -435,6 +435,15 @@ struct dentry *exportfs_decode_fh(struct vfsmount *mnt, struct fid *fid,
if (IS_ERR_OR_NULL(result))
return ERR_PTR(-ESTALE);
/*
* If no acceptance criteria was specified by caller, a disconnected
* dentry is also accepatable. Callers may use this mode to query if
* file handle is stale or to get a reference to an inode without
* risking the high overhead caused by directory reconnect.
*/
if (!acceptable)
return result;
if (d_is_dir(result)) {
/*
* This request is for a directory.

4
fs/overlayfs/export.c
View File

@ -685,7 +685,7 @@ static struct dentry *ovl_upper_fh_to_d(struct super_block *sb,
if (!ofs->upper_mnt)
return ERR_PTR(-EACCES);
upper = ovl_decode_real_fh(fh, ofs->upper_mnt);
upper = ovl_decode_real_fh(fh, ofs->upper_mnt, true);
if (IS_ERR_OR_NULL(upper))
return upper;
@ -735,7 +735,7 @@ static struct dentry *ovl_lower_fh_to_d(struct super_block *sb,
}
/* Then lookup origin by fh */
err = ovl_check_origin_fh(ofs, fh, NULL, &stack);
err = ovl_check_origin_fh(ofs, fh, true, NULL, &stack);
if (err) {
goto out_err;
} else if (index) {

16
fs/overlayfs/namei.c
View File

@ -180,7 +180,8 @@ invalid:
goto out;
}
struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt)
struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
bool connected)
{
struct dentry *real;
int bytes;
@ -195,7 +196,7 @@ struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt)
bytes = (fh->len - offsetof(struct ovl_fh, fid));
real = exportfs_decode_fh(mnt, (struct fid *)fh->fid,
bytes >> 2, (int)fh->type,
ovl_acceptable, mnt);
connected ? ovl_acceptable : NULL, mnt);
if (IS_ERR(real)) {
/*
* Treat stale file handle to lower file as "origin unknown".
@ -319,14 +320,15 @@ static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
}
int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
struct dentry *upperdentry, struct ovl_path **stackp)
{
struct dentry *origin = NULL;
int i;
for (i = 0; i < ofs->numlower; i++) {
origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt);
origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt,
connected);
if (origin)
break;
}
@ -370,7 +372,7 @@ static int ovl_check_origin(struct ovl_fs *ofs, struct dentry *upperdentry,
if (IS_ERR_OR_NULL(fh))
return PTR_ERR(fh);
err = ovl_check_origin_fh(ofs, fh, upperdentry, stackp);
err = ovl_check_origin_fh(ofs, fh, false, upperdentry, stackp);
kfree(fh);
if (err) {
@ -460,7 +462,7 @@ struct dentry *ovl_index_upper(struct ovl_fs *ofs, struct dentry *index)
if (IS_ERR_OR_NULL(fh))
return ERR_CAST(fh);
upper = ovl_decode_real_fh(fh, ofs->upper_mnt);
upper = ovl_decode_real_fh(fh, ofs->upper_mnt, true);
kfree(fh);
if (IS_ERR_OR_NULL(upper))
@ -567,7 +569,7 @@ int ovl_verify_index(struct ovl_fs *ofs, struct dentry *index)
/* Check if non-dir index is orphan and don't warn before cleaning it */
if (!d_is_dir(index) && d_inode(index)->i_nlink == 1) {
err = ovl_check_origin_fh(ofs, fh, index, &stack);
err = ovl_check_origin_fh(ofs, fh, false, index, &stack);
if (err)
goto fail;

5
fs/overlayfs/overlayfs.h
View File

@ -266,8 +266,9 @@ static inline bool ovl_is_impuredir(struct dentry *dentry)
/* namei.c */
int ovl_check_fh_len(struct ovl_fh *fh, int fh_len);
struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt);
int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh,
struct dentry *ovl_decode_real_fh(struct ovl_fh *fh, struct vfsmount *mnt,
bool connected);
int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
struct dentry *upperdentry, struct ovl_path **stackp);
int ovl_verify_set_fh(struct dentry *dentry, const char *name,
struct dentry *real, bool is_upper, bool set);