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SubjectRe: [PATCH 1/4] statx: Add a system call to make enhanced file info available [ver #3]
On Sun, Dec 04, 2016 at 04:38:05AM +0000, Al Viro wrote:

> I understand wanting to avoid extra arguments, but you are asking for trouble
> with that sort of calling conventions. Verifying that all call chains have
> these fields initialized is bloody unpleasant and it *is* going to break,
> especially since the rules are "you need to initialize it for vfs_xgetattr(),
> but not for vfs_getattr()" - the names are similar enough for confusion,
> and that's not the only such pair.

FWIW, there's a bit of abuse of struct kstat in overlayfs object
creation paths - for one thing, it ends up with a very small subset
of struct kstat (mode + rdev), for another it also needs link in
case of symlinks and ends up passing it separately.

IMO it would be better to introduce a separate object for that; does anybody
have objections to something like the patch below? In principle, we might
even lift that thing into general API and switch ->mkdir()/->mknod()/->symlink()
to identical calling conventions. Hell knows, perhaps ->create() as well...
Comments?

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 36795ee..17ad2da 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -231,10 +231,15 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
struct inode *udir = upperdir->d_inode;
struct dentry *newdentry = NULL;
struct dentry *upper = NULL;
- umode_t mode = stat->mode;
int err;
const struct cred *old_creds = NULL;
struct cred *new_creds = NULL;
+ struct cattr cattr = {
+ /* Can't properly set mode on creation because of the umask */
+ .mode = stat->mode & S_IFMT,
+ .rdev = stat->rdev,
+ .link = link
+ };

newdentry = ovl_lookup_temp(workdir, dentry);
err = PTR_ERR(newdentry);
@@ -254,10 +259,7 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
if (new_creds)
old_creds = override_creds(new_creds);

- /* Can't properly set mode on creation because of the umask */
- stat->mode &= S_IFMT;
- err = ovl_create_real(wdir, newdentry, stat, link, NULL, true);
- stat->mode = mode;
+ err = ovl_create_real(wdir, newdentry, &cattr, NULL, true);

if (new_creds) {
revert_creds(old_creds);
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 306b6c1..dc60a23 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -75,8 +75,8 @@ static struct dentry *ovl_whiteout(struct dentry *workdir,
}

int ovl_create_real(struct inode *dir, struct dentry *newdentry,
- struct kstat *stat, const char *link,
- struct dentry *hardlink, bool debug)
+ struct cattr *attr, struct dentry *hardlink,
+ bool debug)
{
int err;

@@ -86,13 +86,13 @@ int ovl_create_real(struct inode *dir, struct dentry *newdentry,
if (hardlink) {
err = ovl_do_link(hardlink, dir, newdentry, debug);
} else {
- switch (stat->mode & S_IFMT) {
+ switch (attr->mode & S_IFMT) {
case S_IFREG:
- err = ovl_do_create(dir, newdentry, stat->mode, debug);
+ err = ovl_do_create(dir, newdentry, attr->mode, debug);
break;

case S_IFDIR:
- err = ovl_do_mkdir(dir, newdentry, stat->mode, debug);
+ err = ovl_do_mkdir(dir, newdentry, attr->mode, debug);
break;

case S_IFCHR:
@@ -100,11 +100,11 @@ int ovl_create_real(struct inode *dir, struct dentry *newdentry,
case S_IFIFO:
case S_IFSOCK:
err = ovl_do_mknod(dir, newdentry,
- stat->mode, stat->rdev, debug);
+ attr->mode, attr->rdev, debug);
break;

case S_IFLNK:
- err = ovl_do_symlink(dir, newdentry, link, debug);
+ err = ovl_do_symlink(dir, newdentry, attr->link, debug);
break;

default:
@@ -183,8 +183,7 @@ static void ovl_instantiate(struct dentry *dentry, struct inode *inode,
}

static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
- struct kstat *stat, const char *link,
- struct dentry *hardlink)
+ struct cattr *attr, struct dentry *hardlink)
{
struct dentry *upperdir = ovl_dentry_upper(dentry->d_parent);
struct inode *udir = upperdir->d_inode;
@@ -192,7 +191,7 @@ static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
int err;

if (!hardlink && !IS_POSIXACL(udir))
- stat->mode &= ~current_umask();
+ attr->mode &= ~current_umask();

inode_lock_nested(udir, I_MUTEX_PARENT);
newdentry = lookup_one_len(dentry->d_name.name, upperdir,
@@ -200,7 +199,7 @@ static int ovl_create_upper(struct dentry *dentry, struct inode *inode,
err = PTR_ERR(newdentry);
if (IS_ERR(newdentry))
goto out_unlock;
- err = ovl_create_real(udir, newdentry, stat, link, hardlink, false);
+ err = ovl_create_real(udir, newdentry, attr, hardlink, false);
if (err)
goto out_dput;

@@ -270,7 +269,8 @@ static struct dentry *ovl_clear_empty(struct dentry *dentry,
if (IS_ERR(opaquedir))
goto out_unlock;

- err = ovl_create_real(wdir, opaquedir, &stat, NULL, NULL, true);
+ err = ovl_create_real(wdir, opaquedir,
+ &(struct cattr){.mode = stat.mode}, NULL, true);
if (err)
goto out_dput;

@@ -370,8 +370,7 @@ static int ovl_set_upper_acl(struct dentry *upperdentry, const char *name,
}

static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
- struct kstat *stat, const char *link,
- struct dentry *hardlink)
+ struct cattr *cattr, struct dentry *hardlink)
{
struct dentry *workdir = ovl_workdir(dentry);
struct inode *wdir = workdir->d_inode;
@@ -387,7 +386,7 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,

if (!hardlink) {
err = posix_acl_create(dentry->d_parent->d_inode,
- &stat->mode, &default_acl, &acl);
+ &cattr->mode, &default_acl, &acl);
if (err)
return err;
}
@@ -407,7 +406,7 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
if (IS_ERR(upper))
goto out_dput;

- err = ovl_create_real(wdir, newdentry, stat, link, hardlink, true);
+ err = ovl_create_real(wdir, newdentry, cattr, hardlink, true);
if (err)
goto out_dput2;

@@ -415,10 +414,10 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
* mode could have been mutilated due to umask (e.g. sgid directory)
*/
if (!hardlink &&
- !S_ISLNK(stat->mode) && newdentry->d_inode->i_mode != stat->mode) {
+ !S_ISLNK(cattr->mode) && newdentry->d_inode->i_mode != cattr->mode) {
struct iattr attr = {
.ia_valid = ATTR_MODE,
- .ia_mode = stat->mode,
+ .ia_mode = cattr->mode,
};
inode_lock(newdentry->d_inode);
err = notify_change(newdentry, &attr, NULL);
@@ -438,7 +437,7 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
goto out_cleanup;
}

- if (!hardlink && S_ISDIR(stat->mode)) {
+ if (!hardlink && S_ISDIR(cattr->mode)) {
err = ovl_set_opaque(newdentry);
if (err)
goto out_cleanup;
@@ -475,8 +474,7 @@ static int ovl_create_over_whiteout(struct dentry *dentry, struct inode *inode,
}

static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
- struct kstat *stat, const char *link,
- struct dentry *hardlink)
+ struct cattr *attr, struct dentry *hardlink)
{
int err;
const struct cred *old_cred;
@@ -494,7 +492,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
override_cred->fsgid = inode->i_gid;
if (!hardlink) {
err = security_dentry_create_files_as(dentry,
- stat->mode, &dentry->d_name, old_cred,
+ attr->mode, &dentry->d_name, old_cred,
override_cred);
if (err) {
put_cred(override_cred);
@@ -505,11 +503,11 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode,
put_cred(override_cred);

if (!ovl_dentry_is_opaque(dentry))
- err = ovl_create_upper(dentry, inode, stat, link,
+ err = ovl_create_upper(dentry, inode, attr,
hardlink);
else
- err = ovl_create_over_whiteout(dentry, inode, stat,
- link, hardlink);
+ err = ovl_create_over_whiteout(dentry, inode, attr,
+ hardlink);
}
out_revert_creds:
revert_creds(old_cred);
@@ -528,8 +526,9 @@ static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
{
int err;
struct inode *inode;
- struct kstat stat = {
+ struct cattr attr = {
.rdev = rdev,
+ .link = link,
};

err = ovl_want_write(dentry);
@@ -542,9 +541,9 @@ static int ovl_create_object(struct dentry *dentry, int mode, dev_t rdev,
goto out_drop_write;

inode_init_owner(inode, dentry->d_parent->d_inode, mode);
- stat.mode = inode->i_mode;
+ attr.mode = inode->i_mode;

- err = ovl_create_or_link(dentry, inode, &stat, link, NULL);
+ err = ovl_create_or_link(dentry, inode, &attr, NULL);
if (err)
iput(inode);

@@ -598,7 +597,7 @@ static int ovl_link(struct dentry *old, struct inode *newdir,
inode = d_inode(old);
ihold(inode);

- err = ovl_create_or_link(new, inode, NULL, NULL, ovl_dentry_upper(old));
+ err = ovl_create_or_link(new, inode, NULL, ovl_dentry_upper(old));
if (err)
iput(inode);

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index e218e74..346b38b 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -210,8 +210,13 @@ static inline void ovl_copyattr(struct inode *from, struct inode *to)
/* dir.c */
extern const struct inode_operations ovl_dir_inode_operations;
struct dentry *ovl_lookup_temp(struct dentry *workdir, struct dentry *dentry);
+struct cattr {
+ dev_t rdev;
+ umode_t mode;
+ const char *link;
+};
int ovl_create_real(struct inode *dir, struct dentry *newdentry,
- struct kstat *stat, const char *link,
+ struct cattr *attr,
struct dentry *hardlink, bool debug);
void ovl_cleanup(struct inode *dir, struct dentry *dentry);

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index edd46a0..c95e447 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -809,12 +809,9 @@ static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
strlen(OVL_WORKDIR_NAME));

if (!IS_ERR(work)) {
- struct kstat stat = {
- .mode = S_IFDIR | 0,
- };
struct iattr attr = {
.ia_valid = ATTR_MODE,
- .ia_mode = stat.mode,
+ .ia_mode = S_IFDIR | 0,
};

if (work->d_inode) {
@@ -828,7 +825,9 @@ static struct dentry *ovl_workdir_create(struct vfsmount *mnt,
goto retry;
}

- err = ovl_create_real(dir, work, &stat, NULL, NULL, true);
+ err = ovl_create_real(dir, work,
+ &(struct cattr){.mode = S_IFDIR | 0},
+ NULL, true);
if (err)
goto out_dput;

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