sysfs, kernfs: introduce kernfs_ops

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 112 insertions, 34 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index acba5835577e..cbebc335af8c 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);