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debugfs: get rid of dynamically allocation proxy_ops

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All it takes is having full_proxy_open() collect the information
about available methods and store it in debugfs_fsdata.

Wrappers are called only after full_proxy_open() has succeeded
calling debugfs_get_file(), so they are guaranteed to have
->d_fsdata already pointing to debugfs_fsdata.

As the result, they can check if method is absent and bugger off
early, without any atomic operations, etc. - same effect as what
we'd have from NULL method.  Which makes the entire proxy_fops
contents unconditional, making it completely pointless - we can
just put those methods (unconditionally) into
debugfs_full_proxy_file_operations and forget about dynamic
allocation, replace_fops, etc.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Link: https://lore.kernel.org/r/20250112080705.141166-3-viro@zeniv.linux.org.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Al Viro 2025-01-12 08:06:47 +00:00 • committed by Greg Kroah-Hartman
parent bacaaf833e
commit 41a0ecc099
2 changed files with 61 additions and 61 deletions
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113
fs/debugfs/file.c
View file

@ -95,13 +95,31 @@ static int __debugfs_file_get(struct dentry *dentry, enum dbgfs_get_mode mode)
return -ENOMEM;
if (mode == DBGFS_GET_SHORT) {
fsd->real_fops = NULL;
fsd->short_fops = (void *)((unsigned long)d_fsd &
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
const struct debugfs_short_fops *ops;
ops = (void *)((unsigned long)d_fsd &
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
fsd->short_fops = ops;
if (ops->llseek)
fsd->methods |= HAS_LSEEK;
if (ops->read)
fsd->methods |= HAS_READ;
if (ops->write)
fsd->methods |= HAS_WRITE;
} else {
fsd->real_fops = (void *)((unsigned long)d_fsd &
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
fsd->short_fops = NULL;
const struct file_operations *ops;
ops = (void *)((unsigned long)d_fsd &
~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
fsd->real_fops = ops;
if (ops->llseek)
fsd->methods |= HAS_LSEEK;
if (ops->read)
fsd->methods |= HAS_READ;
if (ops->write)
fsd->methods |= HAS_WRITE;
if (ops->unlocked_ioctl)
fsd->methods |= HAS_IOCTL;
if (ops->poll)
fsd->methods |= HAS_POLL;
}
refcount_set(&fsd->active_users, 1);
init_completion(&fsd->active_users_drained);
@ -322,13 +340,16 @@ const struct file_operations debugfs_open_proxy_file_operations = {
#define PROTO(args...) args
#define ARGS(args...) args
#define FULL_PROXY_FUNC(name, ret_type, filp, proto, args) \
#define FULL_PROXY_FUNC(name, ret_type, filp, proto, args, bit, ret) \
static ret_type full_proxy_ ## name(proto) \
{ \
struct dentry *dentry = F_DENTRY(filp); \
struct dentry *dentry = F_DENTRY(filp); \
struct debugfs_fsdata *fsd = dentry->d_fsdata; \
const struct file_operations *real_fops; \
ret_type r; \
\
if (!(fsd->methods & bit)) \
return ret; \
r = debugfs_file_get(dentry); \
if (unlikely(r)) \
return r; \
@ -338,17 +359,18 @@ static ret_type full_proxy_ ## name(proto) \
return r; \
}
#define FULL_PROXY_FUNC_BOTH(name, ret_type, filp, proto, args) \
#define FULL_PROXY_FUNC_BOTH(name, ret_type, filp, proto, args, bit, ret) \
static ret_type full_proxy_ ## name(proto) \
{ \
struct dentry *dentry = F_DENTRY(filp); \
struct debugfs_fsdata *fsd; \
struct debugfs_fsdata *fsd = dentry->d_fsdata; \
ret_type r; \
\
if (!(fsd->methods & bit)) \
return ret; \
r = debugfs_file_get(dentry); \
if (unlikely(r)) \
return r; \
fsd = dentry->d_fsdata; \
if (fsd->real_fops) \
r = fsd->real_fops->name(args); \
else \
@ -359,29 +381,32 @@ static ret_type full_proxy_ ## name(proto) \
FULL_PROXY_FUNC_BOTH(llseek, loff_t, filp,
PROTO(struct file *filp, loff_t offset, int whence),
ARGS(filp, offset, whence));
ARGS(filp, offset, whence), HAS_LSEEK, -ESPIPE);
FULL_PROXY_FUNC_BOTH(read, ssize_t, filp,
PROTO(struct file *filp, char __user *buf, size_t size,
loff_t *ppos),
ARGS(filp, buf, size, ppos));
ARGS(filp, buf, size, ppos), HAS_READ, -EINVAL);
FULL_PROXY_FUNC_BOTH(write, ssize_t, filp,
PROTO(struct file *filp, const char __user *buf,
size_t size, loff_t *ppos),
ARGS(filp, buf, size, ppos));
ARGS(filp, buf, size, ppos), HAS_WRITE, -EINVAL);
FULL_PROXY_FUNC(unlocked_ioctl, long, filp,
PROTO(struct file *filp, unsigned int cmd, unsigned long arg),
ARGS(filp, cmd, arg));
ARGS(filp, cmd, arg), HAS_IOCTL, -ENOTTY);
static __poll_t full_proxy_poll(struct file *filp,
struct poll_table_struct *wait)
{
struct dentry *dentry = F_DENTRY(filp);
struct debugfs_fsdata *fsd = dentry->d_fsdata;
__poll_t r = 0;
const struct file_operations *real_fops;
if (!(fsd->methods & HAS_POLL))
return DEFAULT_POLLMASK;
if (debugfs_file_get(dentry))
return EPOLLHUP;
@ -393,9 +418,7 @@ static __poll_t full_proxy_poll(struct file *filp,
static int full_proxy_release(struct inode *inode, struct file *filp)
{
const struct dentry *dentry = F_DENTRY(filp);
const struct file_operations *real_fops = debugfs_real_fops(filp);
const struct file_operations *proxy_fops = filp->f_op;
int r = 0;
/*
@ -407,42 +430,15 @@ static int full_proxy_release(struct inode *inode, struct file *filp)
if (real_fops && real_fops->release)
r = real_fops->release(inode, filp);
replace_fops(filp, d_inode(dentry)->i_fop);
kfree(proxy_fops);
fops_put(real_fops);
return r;
}
static void __full_proxy_fops_init(struct file_operations *proxy_fops,
struct debugfs_fsdata *fsd)
{
proxy_fops->release = full_proxy_release;
if ((fsd->real_fops && fsd->real_fops->llseek) ||
(fsd->short_fops && fsd->short_fops->llseek))
proxy_fops->llseek = full_proxy_llseek;
if ((fsd->real_fops && fsd->real_fops->read) ||
(fsd->short_fops && fsd->short_fops->read))
proxy_fops->read = full_proxy_read;
if ((fsd->real_fops && fsd->real_fops->write) ||
(fsd->short_fops && fsd->short_fops->write))
proxy_fops->write = full_proxy_write;
if (fsd->real_fops && fsd->real_fops->poll)
proxy_fops->poll = full_proxy_poll;
if (fsd->real_fops && fsd->real_fops->unlocked_ioctl)
proxy_fops->unlocked_ioctl = full_proxy_unlocked_ioctl;
}
static int full_proxy_open(struct inode *inode, struct file *filp,
enum dbgfs_get_mode mode)
{
struct dentry *dentry = F_DENTRY(filp);
const struct file_operations *real_fops;
struct file_operations *proxy_fops = NULL;
struct debugfs_fsdata *fsd;
int r;
@ -472,34 +468,20 @@ static int full_proxy_open(struct inode *inode, struct file *filp,
goto out;
}
proxy_fops = kzalloc(sizeof(*proxy_fops), GFP_KERNEL);
if (!proxy_fops) {
r = -ENOMEM;
goto free_proxy;
}
__full_proxy_fops_init(proxy_fops, fsd);
replace_fops(filp, proxy_fops);
if (!real_fops || real_fops->open) {
if (real_fops)
r = real_fops->open(inode, filp);
else
r = simple_open(inode, filp);
if (r) {
replace_fops(filp, d_inode(dentry)->i_fop);
goto free_proxy;
} else if (filp->f_op != proxy_fops) {
fops_put(real_fops);
} else if (filp->f_op != &debugfs_full_proxy_file_operations) {
/* No protection against file removal anymore. */
WARN(1, "debugfs file owner replaced proxy fops: %pd",
dentry);
goto free_proxy;
fops_put(real_fops);
}
}
goto out;
free_proxy:
kfree(proxy_fops);
fops_put(real_fops);
out:
debugfs_file_put(dentry);
return r;
@ -512,6 +494,12 @@ static int full_proxy_open_regular(struct inode *inode, struct file *filp)
const struct file_operations debugfs_full_proxy_file_operations = {
.open = full_proxy_open_regular,
.release = full_proxy_release,
.llseek = full_proxy_llseek,
.read = full_proxy_read,
.write = full_proxy_write,
.poll = full_proxy_poll,
.unlocked_ioctl = full_proxy_unlocked_ioctl
};
static int full_proxy_open_short(struct inode *inode, struct file *filp)
@ -521,6 +509,9 @@ static int full_proxy_open_short(struct inode *inode, struct file *filp)
const struct file_operations debugfs_full_short_proxy_file_operations = {
.open = full_proxy_open_short,
.llseek = full_proxy_llseek,
.read = full_proxy_read,
.write = full_proxy_write,
};
ssize_t debugfs_attr_read(struct file *file, char __user *buf,

9
fs/debugfs/internal.h
View file

@ -39,9 +39,18 @@ struct debugfs_fsdata {
/* protect cancellations */
struct mutex cancellations_mtx;
struct list_head cancellations;
unsigned int methods;
};
};
enum {
HAS_READ = 1,
HAS_WRITE = 2,
HAS_LSEEK = 4,
HAS_POLL = 8,
HAS_IOCTL = 16
};
/*
* A dentry's ->d_fsdata either points to the real fops or to a
* dynamically allocated debugfs_fsdata instance.