[PATCH 08/34] sysfs, kernfs: introduce kernfs_ops

Tejun Heo
2013-11-28T19:55:18Z

We're in the process of separating out core sysfs functionality into
kernfs which will deal with sysfs_dirents directly. This patch
introduces kernfs_ops which hosts methods kernfs users implement and
updates fs/sysfs/file.c such that sysfs_kf_*() functions populate
kernfs_ops and kernfs_file_*() functions call the matching entries
from kernfs_ops.

kernfs_ops contains the following groups of methods.

* seq_show() - for kernfs files which use seq_file for reads.

* read() - for direct read implementations. Used iff seq_show() is
not implemented.

* write() - for writes.

* mmap() - for mmaps.

Notes:

* sysfs_elem_attr->ops is added so that kernfs_ops can be accessed
from sysfs_dirent. kernfs_ops() helper is added to verify locking
and access the field.

* SYSFS_FLAG_HAS_(SEQ_SHOW|MMAP) added. sd->s_attr->ops is accessible
only while holding active_ref and there are cases where we want to
take different actions depending on which ops are implemented.
These two flags cache whether the two ops are implemented for those.

* kernfs_file_*() no longer test sysfs type but chooses different
behaviors depending on which methods in kernfs_ops are implemented.
The conversions are trivial except for the open path. As
kernfs_file_open() now decides whether to allow read/write accesses
depending on the kernfs_ops implemented, the presence of methods in
kobjs and attribute_bin should be propagated to kernfs_ops.
sysfs_add_file_mode_ns() is updated so that it propagates presence /
absence of the callbacks through _empty, _ro, _wo, _rw kernfs_ops.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
fs/sysfs/file.c | 146 +++++++++++++++++++++++++++++++++++++------------
fs/sysfs/sysfs.h | 3 +
include/linux/kernfs.h | 26 +++++++++
3 files changed, 141 insertions(+), 34 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index acba583..cbebc33 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -58,6 +58,17 @@ static struct sysfs_open_file *sysfs_of(struct file *file)
}

/*
+ * Determine the kernfs_ops for the given sysfs_dirent. This function must
+ * be called while holding an active reference.
+ */
+static const struct kernfs_ops *kernfs_ops(struct sysfs_dirent *sd)
+{
+ if (!sysfs_ignore_lockdep(sd))
+ lockdep_assert_held(sd);
+ return sd->s_attr.ops;
+}
+
+/*
* Determine ktype->sysfs_ops for the given sysfs_dirent. This function
* must be called while holding an active reference.
*/
@@ -180,7 +191,7 @@ static int kernfs_seq_show(struct seq_file *sf, void *v)

of->event = atomic_read(&of->sd->s_attr.open->event);

- return sysfs_kf_seq_show(sf, v);
+ return of->sd->s_attr.ops->seq_show(sf, v);
}

static const struct seq_operations kernfs_seq_ops = {
@@ -201,6 +212,7 @@ static ssize_t kernfs_file_direct_read(struct sysfs_open_file *of,
loff_t *ppos)
{
ssize_t len = min_t(size_t, count, PAGE_SIZE);
+ const struct kernfs_ops *ops;
char *buf;

buf = kmalloc(len, GFP_KERNEL);
@@ -218,7 +230,11 @@ static ssize_t kernfs_file_direct_read(struct sysfs_open_file *of,
goto out_free;
}

- len = sysfs_kf_bin_read(of, buf, len, *ppos);
+ ops = kernfs_ops(of->sd);
+ if (ops->read)
+ len = ops->read(of, buf, len, *ppos);
+ else
+ len = -EINVAL;

sysfs_put_active(of->sd);
mutex_unlock(&of->mutex);
@@ -250,10 +266,10 @@ static ssize_t kernfs_file_read(struct file *file, char __user *user_buf,
{
struct sysfs_open_file *of = sysfs_of(file);

- if (sysfs_is_bin(of->sd))
- return kernfs_file_direct_read(of, user_buf, count, ppos);
- else
+ if (of->sd->s_flags & SYSFS_FLAG_HAS_SEQ_SHOW)
return seq_read(file, user_buf, count, ppos);
+ else
+ return kernfs_file_direct_read(of, user_buf, count, ppos);
}

/* kernfs write callback for regular sysfs files */
@@ -312,6 +328,7 @@ static ssize_t kernfs_file_write(struct file *file, const char __user *user_buf,
{
struct sysfs_open_file *of = sysfs_of(file);
ssize_t len = min_t(size_t, count, PAGE_SIZE);
+ const struct kernfs_ops *ops;
char *buf;

buf = kmalloc(len + 1, GFP_KERNEL);
@@ -335,10 +352,11 @@ static ssize_t kernfs_file_write(struct file *file, const char __user *user_buf,
goto out_free;
}

- if (sysfs_is_bin(of->sd))
- len = sysfs_kf_bin_write(of, buf, len, *ppos);
+ ops = kernfs_ops(of->sd);
+ if (ops->write)
+ len = ops->write(of, buf, len, *ppos);
else
- len = sysfs_kf_write(of, buf, len, *ppos);
+ len = -EINVAL;

sysfs_put_active(of->sd);
mutex_unlock(&of->mutex);
@@ -524,6 +542,7 @@ static const struct vm_operations_struct kernfs_vm_ops = {
static int kernfs_file_mmap(struct file *file, struct vm_area_struct *vma)
{
struct sysfs_open_file *of = sysfs_of(file);
+ const struct kernfs_ops *ops;
int rc;

mutex_lock(&of->mutex);
@@ -532,8 +551,9 @@ static int kernfs_file_mmap(struct file *file, struct vm_area_struct *vma)
if (!sysfs_get_active(of->sd))
goto out_unlock;

- if (sysfs_is_bin(of->sd))
- rc = sysfs_kf_bin_mmap(of, vma);
+ ops = kernfs_ops(of->sd);
+ if (ops->mmap)
+ rc = ops->mmap(of, vma);
if (rc)
goto out_put;

@@ -660,34 +680,19 @@ static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
static int kernfs_file_open(struct inode *inode, struct file *file)
{
struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata;
- struct kobject *kobj = attr_sd->s_parent->priv;
+ const struct kernfs_ops *ops;
struct sysfs_open_file *of;
bool has_read, has_write, has_mmap;
int error = -EACCES;

- /* need attr_sd for attr and ops, its parent for kobj */
if (!sysfs_get_active(attr_sd))
return -ENODEV;

- if (sysfs_is_bin(attr_sd)) {
- struct bin_attribute *battr = attr_sd->priv;
+ ops = kernfs_ops(attr_sd);

- has_read = battr->read || battr->mmap;
- has_write = battr->write || battr->mmap;
- has_mmap = battr->mmap;
- } else {
- const struct sysfs_ops *ops = sysfs_file_ops(attr_sd);
-
- /* every kobject with an attribute needs a ktype assigned */
- if (WARN(!ops, KERN_ERR
- "missing sysfs attribute operations for kobject: %s\n",
- kobject_name(kobj)))
- goto err_out;
-
- has_read = ops->show;
- has_write = ops->store;
- has_mmap = false;
- }
+ has_read = ops->seq_show || ops->read || ops->mmap;
+ has_write = ops->write || ops->mmap;
+ has_mmap = ops->mmap;

/* check perms and supported operations */
if ((file->f_mode & FMODE_WRITE) &&
@@ -729,10 +734,10 @@ static int kernfs_file_open(struct inode *inode, struct file *file)
* seq_file or is not requested. This unifies private data access
* and readable regular files are the vast majority anyway.
*/
- if (sysfs_is_bin(attr_sd))
- error = seq_open(file, NULL);
- else
+ if (ops->seq_show)
error = seq_open(file, &kernfs_seq_ops);
+ else
+ error = seq_open(file, NULL);
if (error)
goto err_free;

@@ -777,7 +782,7 @@ void sysfs_unmap_bin_file(struct sysfs_dirent *sd)
struct sysfs_open_dirent *od;
struct sysfs_open_file *of;

- if (!sysfs_is_bin(sd))
+ if (!(sd->s_flags & SYSFS_FLAG_HAS_MMAP))
return;

spin_lock_irq(&sysfs_open_dirent_lock);
@@ -880,23 +885,96 @@ const struct file_operations kernfs_file_operations = {
.poll = kernfs_file_poll,
};

+static const struct kernfs_ops sysfs_file_kfops_empty = {
+};
+
+static const struct kernfs_ops sysfs_file_kfops_ro = {
+ .seq_show = sysfs_kf_seq_show,
+};
+
+static const struct kernfs_ops sysfs_file_kfops_wo = {
+ .write = sysfs_kf_write,
+};
+
+static const struct kernfs_ops sysfs_file_kfops_rw = {
+ .seq_show = sysfs_kf_seq_show,
+ .write = sysfs_kf_write,
+};
+
+static const struct kernfs_ops sysfs_bin_kfops_ro = {
+ .read = sysfs_kf_bin_read,
+};
+
+static const struct kernfs_ops sysfs_bin_kfops_wo = {
+ .write = sysfs_kf_bin_write,
+};
+
+static const struct kernfs_ops sysfs_bin_kfops_rw = {
+ .read = sysfs_kf_bin_read,
+ .write = sysfs_kf_bin_write,
+ .mmap = sysfs_kf_bin_mmap,
+};
+
int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
const struct attribute *attr, int type,
umode_t amode, const void *ns)
{
umode_t mode = (amode & S_IALLUGO) | S_IFREG;
+ const struct kernfs_ops *ops;
struct sysfs_addrm_cxt acxt;
struct sysfs_dirent *sd;
int rc;

+ if (type == SYSFS_KOBJ_ATTR) {
+ struct kobject *kobj = dir_sd->priv;
+ const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;
+
+ /* every kobject with an attribute needs a ktype assigned */
+ if (WARN(!sysfs_ops, KERN_ERR
+ "missing sysfs attribute operations for kobject: %s\n",
+ kobject_name(kobj)))
+ return -EINVAL;
+
+ if (sysfs_ops->show && sysfs_ops->store)
+ ops = &sysfs_file_kfops_rw;
+ else if (sysfs_ops->show)
+ ops = &sysfs_file_kfops_ro;
+ else if (sysfs_ops->store)
+ ops = &sysfs_file_kfops_wo;
+ else
+ ops = &sysfs_file_kfops_empty;
+ } else {
+ struct bin_attribute *battr = (void *)attr;
+
+ if ((battr->read && battr->write) || battr->mmap)
+ ops = &sysfs_bin_kfops_rw;
+ else if (battr->read)
+ ops = &sysfs_bin_kfops_ro;
+ else if (battr->write)
+ ops = &sysfs_bin_kfops_wo;
+ else
+ ops = &sysfs_file_kfops_empty;
+ }
+
sd = sysfs_new_dirent(attr->name, mode, type);
if (!sd)
return -ENOMEM;

+ sd->s_attr.ops = ops;
sd->s_ns = ns;
sd->priv = (void *)attr;
sysfs_dirent_init_lockdep(sd);

+ /*
+ * sd->s_attr.ops is accesible only while holding active ref. We
+ * need to know whether some ops are implemented outside active
+ * ref. Cache their existence in flags.
+ */
+ if (ops->seq_show)
+ sd->s_flags |= SYSFS_FLAG_HAS_SEQ_SHOW;
+ if (ops->mmap)
+ sd->s_flags |= SYSFS_FLAG_HAS_MMAP;
+
sysfs_addrm_start(&acxt);
rc = sysfs_add_one(&acxt, sd, dir_sd);
sysfs_addrm_finish(&acxt);
diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 619250d..c05e0dd 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -27,6 +27,7 @@ struct sysfs_elem_symlink {
};

struct sysfs_elem_attr {
+ const struct kernfs_ops *ops;
struct sysfs_open_dirent *open;
};

@@ -89,6 +90,8 @@ struct sysfs_dirent {
#define SYSFS_FLAG_MASK ~SYSFS_TYPE_MASK
#define SYSFS_FLAG_NS 0x01000
#define SYSFS_FLAG_REMOVED 0x02000
+#define SYSFS_FLAG_HAS_SEQ_SHOW 0x04000
+#define SYSFS_FLAG_HAS_MMAP 0x08000

static inline unsigned int sysfs_type(struct sysfs_dirent *sd)
{
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index b923052..97c6c0f 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -33,6 +33,32 @@ struct sysfs_open_file {
const struct vm_operations_struct *vm_ops;
};

+struct kernfs_ops {
+ /*
+ * Read is handled by either seq_file or raw_read().
+ *
+ * If seq_show() is present, seq_file path is active. The behavior
+ * is equivalent to single_open(). @sf->private points to the
+ * associated sysfs_open_file.
+ *
+ * read() is bounced through kernel buffer and a read larger than
+ * PAGE_SIZE results in partial operation of PAGE_SIZE.
+ */
+ int (*seq_show)(struct seq_file *sf, void *v);
+
+ ssize_t (*read)(struct sysfs_open_file *of, char *buf, size_t bytes,
+ loff_t off);
+
+ /*
+ * write() is bounced through kernel buffer and a write larger than
+ * PAGE_SIZE results in partial operation of PAGE_SIZE.
+ */
+ ssize_t (*write)(struct sysfs_open_file *of, char *buf, size_t bytes,
+ loff_t off);
+
+ int (*mmap)(struct sysfs_open_file *of, struct vm_area_struct *vma);
+};
+
#ifdef CONFIG_SYSFS

struct sysfs_dirent *kernfs_create_dir_ns(struct sysfs_dirent *parent,
--
1.8.4.2