/* * file.c - operations for regular (text) files. */ #include <linux/module.h>#include <linux/fsnotify.h>#include <linux/kobject.h>#include <linux/namei.h>#include <linux/poll.h>#include <asm/uaccess.h>#include <asm/semaphore.h> #include "sysfs.h" #define to_subsys(k) container_of(k,struct subsystem,kset.kobj)#define to_sattr(a) container_of(a,struct subsys_attribute,attr) /* * Subsystem file operations. * These operations allow subsystems to have files that can be * read/written. */static ssize_t subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page){ struct subsystem * s = to_subsys(kobj); struct subsys_attribute * sattr = to_sattr(attr); ssize_t ret = -EIO; if (sattr->show) ret = sattr->show(s,page); return ret;} static ssize_t subsys_attr_store(struct kobject * kobj, struct attribute * attr, const char * page, size_t count){ struct subsystem * s = to_subsys(kobj); struct subsys_attribute * sattr = to_sattr(attr); ssize_t ret = -EIO; if (sattr->store) ret = sattr->store(s,page,count); return ret;} static struct sysfs_ops subsys_sysfs_ops = { .show = subsys_attr_show, .store = subsys_attr_store,}; struct sysfs_buffer { size_t count; loff_t pos; char * page; struct sysfs_ops * ops; struct semaphore sem; int needs_read_fill; int event;}; /** * fill_read_buffer - allocate and fill buffer from object. * @dentry: dentry pointer. * @buffer: data buffer for file. * * Allocate @buffer->page, if it hasn't been already, then call the * kobject's show() method to fill the buffer with this attribute's * data. * This is called only once, on the file's first read. */static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer){ struct sysfs_dirent * sd = dentry->d_fsdata; struct attribute * attr = to_attr(dentry); struct kobject * kobj = to_kobj(dentry->d_parent); struct sysfs_ops * ops = buffer->ops; int ret = 0; ssize_t count; if (!buffer->page) buffer->page = (char *) get_zeroed_page(GFP_KERNEL); if (!buffer->page) return -ENOMEM; buffer->event = atomic_read(&sd->s_event); count = ops->show(kobj,attr,buffer->page); buffer->needs_read_fill = 0; BUG_ON(count > (ssize_t)PAGE_SIZE); if (count >= 0) buffer->count = count; else ret = count; return ret;} /** * flush_read_buffer - push buffer to userspace. * @buffer: data buffer for file. * @buf: user-passed buffer. * @count: number of bytes requested. * @ppos: file position. * * Copy the buffer we filled in fill_read_buffer() to userspace. * This is done at the reader's leisure, copying and advancing * the amount they specify each time. * This may be called continuously until the buffer is empty. */static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf, size_t count, loff_t * ppos){ int error; if (*ppos > buffer->count) return 0; if (count > (buffer->count - *ppos)) count = buffer->count - *ppos; error = copy_to_user(buf,buffer->page + *ppos,count); if (!error) *ppos += count; return error ? -EFAULT : count;} /** * sysfs_read_file - read an attribute. * @file: file pointer. * @buf: buffer to fill. * @count: number of bytes to read. * @ppos: starting offset in file. * * Userspace wants to read an attribute file. The attribute descriptor * is in the file's ->d_fsdata. The target object is in the directory's * ->d_fsdata. * * We call fill_read_buffer() to allocate and fill the buffer from the * object's show() method exactly once (if the read is happening from * the beginning of the file). That should fill the entire buffer with * all the data the object has to offer for that attribute. * We then call flush_read_buffer() to copy the buffer to userspace * in the increments specified. */ static ssize_tsysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos){ struct sysfs_buffer * buffer = file->private_data; ssize_t retval = 0; down(&buffer->sem); if (buffer->needs_read_fill) { if ((retval = fill_read_buffer(file->f_dentry,buffer))) goto out; } pr_debug("%s: count = %d, ppos = %lld, buf = %s\n", __FUNCTION__,count,*ppos,buffer->page); retval = flush_read_buffer(buffer,buf,count,ppos);out: up(&buffer->sem); return retval;} /** * fill_write_buffer - copy buffer from userspace. * @buffer: data buffer for file. * @buf: data from user. * @count: number of bytes in @userbuf. * * Allocate @buffer->page if it hasn't been already, then * copy the user-supplied buffer into it. */ static int fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count){ int error; if (!buffer->page) buffer->page = (char *)get_zeroed_page(GFP_KERNEL); if (!buffer->page) return -ENOMEM; if (count >= PAGE_SIZE) count = PAGE_SIZE - 1; error = copy_from_user(buffer->page,buf,count); buffer->needs_read_fill = 1; return error ? -EFAULT : count;} /** * flush_write_buffer - push buffer to kobject. * @dentry: dentry to the attribute * @buffer: data buffer for file. * @count: number of bytes * * Get the correct pointers for the kobject and the attribute we're * dealing with, then call the store() method for the attribute, * passing the buffer that we acquired in fill_write_buffer(). */ static int flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count){ struct attribute * attr = to_attr(dentry); struct kobject * kobj = to_kobj(dentry->d_parent); struct sysfs_ops * ops = buffer->ops; return ops->store(kobj,attr,buffer->page,count);} /** * sysfs_write_file - write an attribute. * @file: file pointer * @buf: data to write * @count: number of bytes * @ppos: starting offset * * Similar to sysfs_read_file(), though working in the opposite direction. * We allocate and fill the data from the user in fill_write_buffer(), * then push it to the kobject in flush_write_buffer(). * There is no easy way for us to know if userspace is only doing a partial * write, so we don't support them. We expect the entire buffer to come * on the first write. * Hint: if you're writing a value, first read the file, modify only the * the value you're changing, then write entire buffer back. */ static ssize_tsysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos){ struct sysfs_buffer * buffer = file->private_data; ssize_t len; down(&buffer->sem); len = fill_write_buffer(buffer, buf, count); if (len > 0) len = flush_write_buffer(file->f_dentry, buffer, len); if (len > 0) *ppos += len; up(&buffer->sem); return len;} static int check_perm(struct inode * inode, struct file * file){ struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent); struct attribute * attr = to_attr(file->f_dentry); struct sysfs_buffer * buffer; struct sysfs_ops * ops = NULL; int error = 0; if (!kobj || !attr) goto Einval; /* Grab the module reference for this attribute if we have one */ if (!try_module_get(attr->owner)) { error = -ENODEV; goto Done; } /* if the kobject has no ktype, then we assume that it is a subsystem * itself, and use ops for it. */ if (kobj->kset && kobj->kset->ktype) ops = kobj->kset->ktype->sysfs_ops; else if (kobj->ktype) ops = kobj->ktype->sysfs_ops; else ops = &subsys_sysfs_ops; /* No sysfs operations, either from having no subsystem, * or the subsystem have no operations. */ if (!ops) goto Eaccess; /* File needs write support. * The inode's perms must say it's ok, * and we must have a store method. */ if (file->f_mode & FMODE_WRITE) { if (!(inode->i_mode & S_IWUGO) || !ops->store) goto Eaccess; } /* File needs read support. * The inode's perms must say it's ok, and we there * must be a show method for it. */ if (file->f_mode & FMODE_READ) { if (!(inode->i_mode & S_IRUGO) || !ops->show) goto Eaccess; } /* No error? Great, allocate a buffer for the file, and store it * it in file->private_data for easy access. */ buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL); if (buffer) { init_MUTEX(&buffer->sem); buffer->needs_read_fill = 1; buffer->ops = ops; file->private_data = buffer; } else error = -ENOMEM; goto Done; Einval: error = -EINVAL; goto Done; Eaccess: error = -EACCES; module_put(attr->owner); Done: if (error && kobj) kobject_put(kobj); return error;} static int sysfs_open_file(struct inode * inode, struct file * filp){ return check_perm(inode,filp);} static int sysfs_release(struct inode * inode, struct file * filp){ struct kobject * kobj = to_kobj(filp->f_dentry->d_parent); struct attribute * attr = to_attr(filp->f_dentry); struct module * owner = attr->owner; struct sysfs_buffer * buffer = filp->private_data; if (kobj) kobject_put(kobj); /* After this point, attr should not be accessed. */ module_put(owner); if (buffer) { if (buffer->page) free_page((unsigned long)buffer->page); kfree(buffer); } return 0;} /* Sysfs attribute files are pollable. The idea is that you read * the content and then you use 'poll' or 'select' to wait for * the content to change. When the content changes (assuming the * manager for the kobject supports notification), poll will * return POLLERR|POLLPRI, and select will return the fd whether * it is waiting for read, write, or exceptions. * Once poll/select indicates that the value has changed, you * need to close and re-open the file, as simply seeking and reading * again will not get new data, or reset the state of 'poll'. * Reminder: this only works for attributes which actively support * it, and it is not possible to test an attribute from userspace * to see if it supports poll (Nether 'poll' or 'select' return * an appropriate error code). When in doubt, set a suitable timeout value. */static unsigned int sysfs_poll(struct file *filp, poll_table *wait){ struct sysfs_buffer * buffer = filp->private_data; struct kobject * kobj = to_kobj(filp->f_dentry->d_parent); struct sysfs_dirent * sd = filp->f_dentry->d_fsdata; int res = 0; poll_wait(filp, &kobj->poll, wait); if (buffer->event != atomic_read(&sd->s_event)) { res = POLLERR|POLLPRI; buffer->needs_read_fill = 1; } return res;} static struct dentry *step_down(struct dentry *dir, const char * name){ struct dentry * de; if (dir == NULL || dir->d_inode == NULL) return NULL; mutex_lock(&dir->d_inode->i_mutex); de = lookup_one_len(name, dir, strlen(name)); mutex_unlock(&dir->d_inode->i_mutex); dput(dir); if (IS_ERR(de)) return NULL; if (de->d_inode == NULL) { dput(de); return NULL; } return de;} void sysfs_notify(struct kobject * k, char *dir, char *attr){ struct dentry *de = k->dentry; if (de) dget(de); if (de && dir) de = step_down(de, dir); if (de && attr) de = step_down(de, attr); if (de) { struct sysfs_dirent * sd = de->d_fsdata; if (sd) atomic_inc(&sd->s_event); wake_up_interruptible(&k->poll); dput(de); }}EXPORT_SYMBOL_GPL(sysfs_notify); const struct file_operations sysfs_file_operations = { .read = sysfs_read_file, .write = sysfs_write_file, .llseek = generic_file_llseek, .open = sysfs_open_file, .release = sysfs_release, .poll = sysfs_poll,}; int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type){ struct sysfs_dirent * parent_sd = dir->d_fsdata; umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG; int error = -EEXIST; mutex_lock(&dir->d_inode->i_mutex); if (!sysfs_dirent_exist(parent_sd, attr->name)) error = sysfs_make_dirent(parent_sd, NULL, (void *)attr, mode, type); mutex_unlock(&dir->d_inode->i_mutex); return error;} /** * sysfs_create_file - create an attribute file for an object. * @kobj: object we're creating for. * @attr: atrribute descriptor. */ int sysfs_create_file(struct kobject * kobj, const struct attribute * attr){ BUG_ON(!kobj || !kobj->dentry || !attr); return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR); } /** * sysfs_update_file - update the modified timestamp on an object attribute. * @kobj: object we're acting for. * @attr: attribute descriptor. */int sysfs_update_file(struct kobject * kobj, const struct attribute * attr){ struct dentry * dir = kobj->dentry; struct dentry * victim; int res = -ENOENT; mutex_lock(&dir->d_inode->i_mutex); victim = lookup_one_len(attr->name, dir, strlen(attr->name)); if (!IS_ERR(victim)) { /* make sure dentry is really there */ if (victim->d_inode && (victim->d_parent->d_inode == dir->d_inode)) { victim->d_inode->i_mtime = CURRENT_TIME; fsnotify_modify(victim); /** * Drop reference from initial sysfs_get_dentry(). */ dput(victim); res = 0; } else d_drop(victim); /** * Drop the reference acquired from sysfs_get_dentry() above. */ dput(victim); } mutex_unlock(&dir->d_inode->i_mutex);Lines 1–500 of 559. Load more
/* * file.c - operations for regular (text) files. */ #include <linux/module.h> #include <linux/fsnotify.h> #include <linux/kobject.h> #include <linux/namei.h> #include <linux/poll.h> #include <asm/uaccess.h> #include <asm/semaphore.h> #include "sysfs.h" #define to_subsys(k) container_of(k,struct subsystem,kset.kobj) #define to_sattr(a) container_of(a,struct subsys_attribute,attr) /* * Subsystem file operations. * These operations allow subsystems to have files that can be * read/written. */ static ssize_t subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page) { struct subsystem * s = to_subsys(kobj); struct subsys_attribute * sattr = to_sattr(attr); ssize_t ret = -EIO; if (sattr->show) ret = sattr->show(s,page); return ret; } static ssize_t subsys_attr_store(struct kobject * kobj, struct attribute * attr, const char * page, size_t count) { struct subsystem * s = to_subsys(kobj); struct subsys_attribute * sattr = to_sattr(attr); ssize_t ret = -EIO; if (sattr->store) ret = sattr->store(s,page,count); return ret; } static struct sysfs_ops subsys_sysfs_ops = { .show = subsys_attr_show, .store = subsys_attr_store, }; struct sysfs_buffer { size_t count; loff_t pos; char * page; struct sysfs_ops * ops; struct semaphore sem; int needs_read_fill; int event; }; /** * fill_read_buffer - allocate and fill buffer from object. * @dentry: dentry pointer. * @buffer: data buffer for file. * * Allocate @buffer->page, if it hasn't been already, then call the * kobject's show() method to fill the buffer with this attribute's * data. * This is called only once, on the file's first read. */ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer) { struct sysfs_dirent * sd = dentry->d_fsdata; struct attribute * attr = to_attr(dentry); struct kobject * kobj = to_kobj(dentry->d_parent); struct sysfs_ops * ops = buffer->ops; int ret = 0; ssize_t count; if (!buffer->page) buffer->page = (char *) get_zeroed_page(GFP_KERNEL); if (!buffer->page) return -ENOMEM; buffer->event = atomic_read(&sd->s_event); count = ops->show(kobj,attr,buffer->page); buffer->needs_read_fill = 0; BUG_ON(count > (ssize_t)PAGE_SIZE); if (count >= 0) buffer->count = count; else ret = count; return ret; } /** * flush_read_buffer - push buffer to userspace. * @buffer: data buffer for file. * @buf: user-passed buffer. * @count: number of bytes requested. * @ppos: file position. * * Copy the buffer we filled in fill_read_buffer() to userspace. * This is done at the reader's leisure, copying and advancing * the amount they specify each time. * This may be called continuously until the buffer is empty. */ static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf, size_t count, loff_t * ppos) { int error; if (*ppos > buffer->count) return 0; if (count > (buffer->count - *ppos)) count = buffer->count - *ppos; error = copy_to_user(buf,buffer->page + *ppos,count); if (!error) *ppos += count; return error ? -EFAULT : count; } /** * sysfs_read_file - read an attribute. * @file: file pointer. * @buf: buffer to fill. * @count: number of bytes to read. * @ppos: starting offset in file. * * Userspace wants to read an attribute file. The attribute descriptor * is in the file's ->d_fsdata. The target object is in the directory's * ->d_fsdata. * * We call fill_read_buffer() to allocate and fill the buffer from the * object's show() method exactly once (if the read is happening from * the beginning of the file). That should fill the entire buffer with * all the data the object has to offer for that attribute. * We then call flush_read_buffer() to copy the buffer to userspace * in the increments specified. */ static ssize_t sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos) { struct sysfs_buffer * buffer = file->private_data; ssize_t retval = 0; down(&buffer->sem); if (buffer->needs_read_fill) { if ((retval = fill_read_buffer(file->f_dentry,buffer))) goto out; } pr_debug("%s: count = %d, ppos = %lld, buf = %s\n", __FUNCTION__,count,*ppos,buffer->page); retval = flush_read_buffer(buffer,buf,count,ppos); out: up(&buffer->sem); return retval; } /** * fill_write_buffer - copy buffer from userspace. * @buffer: data buffer for file. * @buf: data from user. * @count: number of bytes in @userbuf. * * Allocate @buffer->page if it hasn't been already, then * copy the user-supplied buffer into it. */ static int fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count) { int error; if (!buffer->page) buffer->page = (char *)get_zeroed_page(GFP_KERNEL); if (!buffer->page) return -ENOMEM; if (count >= PAGE_SIZE) count = PAGE_SIZE - 1; error = copy_from_user(buffer->page,buf,count); buffer->needs_read_fill = 1; return error ? -EFAULT : count; } /** * flush_write_buffer - push buffer to kobject. * @dentry: dentry to the attribute * @buffer: data buffer for file. * @count: number of bytes * * Get the correct pointers for the kobject and the attribute we're * dealing with, then call the store() method for the attribute, * passing the buffer that we acquired in fill_write_buffer(). */ static int flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count) { struct attribute * attr = to_attr(dentry); struct kobject * kobj = to_kobj(dentry->d_parent); struct sysfs_ops * ops = buffer->ops; return ops->store(kobj,attr,buffer->page,count); } /** * sysfs_write_file - write an attribute. * @file: file pointer * @buf: data to write * @count: number of bytes * @ppos: starting offset * * Similar to sysfs_read_file(), though working in the opposite direction. * We allocate and fill the data from the user in fill_write_buffer(), * then push it to the kobject in flush_write_buffer(). * There is no easy way for us to know if userspace is only doing a partial * write, so we don't support them. We expect the entire buffer to come * on the first write. * Hint: if you're writing a value, first read the file, modify only the * the value you're changing, then write entire buffer back. */ static ssize_t sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos) { struct sysfs_buffer * buffer = file->private_data; ssize_t len; down(&buffer->sem); len = fill_write_buffer(buffer, buf, count); if (len > 0) len = flush_write_buffer(file->f_dentry, buffer, len); if (len > 0) *ppos += len; up(&buffer->sem); return len; } static int check_perm(struct inode * inode, struct file * file) { struct kobject *kobj = sysfs_get_kobject(file->f_dentry->d_parent); struct attribute * attr = to_attr(file->f_dentry); struct sysfs_buffer * buffer; struct sysfs_ops * ops = NULL; int error = 0; if (!kobj || !attr) goto Einval; /* Grab the module reference for this attribute if we have one */ if (!try_module_get(attr->owner)) { error = -ENODEV; goto Done; } /* if the kobject has no ktype, then we assume that it is a subsystem * itself, and use ops for it. */ if (kobj->kset && kobj->kset->ktype) ops = kobj->kset->ktype->sysfs_ops; else if (kobj->ktype) ops = kobj->ktype->sysfs_ops; else ops = &subsys_sysfs_ops; /* No sysfs operations, either from having no subsystem, * or the subsystem have no operations. */ if (!ops) goto Eaccess; /* File needs write support. * The inode's perms must say it's ok, * and we must have a store method. */ if (file->f_mode & FMODE_WRITE) { if (!(inode->i_mode & S_IWUGO) || !ops->store) goto Eaccess; } /* File needs read support. * The inode's perms must say it's ok, and we there * must be a show method for it. */ if (file->f_mode & FMODE_READ) { if (!(inode->i_mode & S_IRUGO) || !ops->show) goto Eaccess; } /* No error? Great, allocate a buffer for the file, and store it * it in file->private_data for easy access. */ buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL); if (buffer) { init_MUTEX(&buffer->sem); buffer->needs_read_fill = 1; buffer->ops = ops; file->private_data = buffer; } else error = -ENOMEM; goto Done; Einval: error = -EINVAL; goto Done; Eaccess: error = -EACCES; module_put(attr->owner); Done: if (error && kobj) kobject_put(kobj); return error; } static int sysfs_open_file(struct inode * inode, struct file * filp) { return check_perm(inode,filp); } static int sysfs_release(struct inode * inode, struct file * filp) { struct kobject * kobj = to_kobj(filp->f_dentry->d_parent); struct attribute * attr = to_attr(filp->f_dentry); struct module * owner = attr->owner; struct sysfs_buffer * buffer = filp->private_data; if (kobj) kobject_put(kobj); /* After this point, attr should not be accessed. */ module_put(owner); if (buffer) { if (buffer->page) free_page((unsigned long)buffer->page); kfree(buffer); } return 0; } /* Sysfs attribute files are pollable. The idea is that you read * the content and then you use 'poll' or 'select' to wait for * the content to change. When the content changes (assuming the * manager for the kobject supports notification), poll will * return POLLERR|POLLPRI, and select will return the fd whether * it is waiting for read, write, or exceptions. * Once poll/select indicates that the value has changed, you * need to close and re-open the file, as simply seeking and reading * again will not get new data, or reset the state of 'poll'. * Reminder: this only works for attributes which actively support * it, and it is not possible to test an attribute from userspace * to see if it supports poll (Nether 'poll' or 'select' return * an appropriate error code). When in doubt, set a suitable timeout value. */ static unsigned int sysfs_poll(struct file *filp, poll_table *wait) { struct sysfs_buffer * buffer = filp->private_data; struct kobject * kobj = to_kobj(filp->f_dentry->d_parent); struct sysfs_dirent * sd = filp->f_dentry->d_fsdata; int res = 0; poll_wait(filp, &kobj->poll, wait); if (buffer->event != atomic_read(&sd->s_event)) { res = POLLERR|POLLPRI; buffer->needs_read_fill = 1; } return res; } static struct dentry *step_down(struct dentry *dir, const char * name) { struct dentry * de; if (dir == NULL || dir->d_inode == NULL) return NULL; mutex_lock(&dir->d_inode->i_mutex); de = lookup_one_len(name, dir, strlen(name)); mutex_unlock(&dir->d_inode->i_mutex); dput(dir); if (IS_ERR(de)) return NULL; if (de->d_inode == NULL) { dput(de); return NULL; } return de; } void sysfs_notify(struct kobject * k, char *dir, char *attr) { struct dentry *de = k->dentry; if (de) dget(de); if (de && dir) de = step_down(de, dir); if (de && attr) de = step_down(de, attr); if (de) { struct sysfs_dirent * sd = de->d_fsdata; if (sd) atomic_inc(&sd->s_event); wake_up_interruptible(&k->poll); dput(de); } } EXPORT_SYMBOL_GPL(sysfs_notify); const struct file_operations sysfs_file_operations = { .read = sysfs_read_file, .write = sysfs_write_file, .llseek = generic_file_llseek, .open = sysfs_open_file, .release = sysfs_release, .poll = sysfs_poll, }; int sysfs_add_file(struct dentry * dir, const struct attribute * attr, int type) { struct sysfs_dirent * parent_sd = dir->d_fsdata; umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG; int error = -EEXIST; mutex_lock(&dir->d_inode->i_mutex); if (!sysfs_dirent_exist(parent_sd, attr->name)) error = sysfs_make_dirent(parent_sd, NULL, (void *)attr, mode, type); mutex_unlock(&dir->d_inode->i_mutex); return error; } /** * sysfs_create_file - create an attribute file for an object. * @kobj: object we're creating for. * @attr: atrribute descriptor. */ int sysfs_create_file(struct kobject * kobj, const struct attribute * attr) { BUG_ON(!kobj || !kobj->dentry || !attr); return sysfs_add_file(kobj->dentry, attr, SYSFS_KOBJ_ATTR); } /** * sysfs_update_file - update the modified timestamp on an object attribute. * @kobj: object we're acting for. * @attr: attribute descriptor. */ int sysfs_update_file(struct kobject * kobj, const struct attribute * attr) { struct dentry * dir = kobj->dentry; struct dentry * victim; int res = -ENOENT; mutex_lock(&dir->d_inode->i_mutex); victim = lookup_one_len(attr->name, dir, strlen(attr->name)); if (!IS_ERR(victim)) { /* make sure dentry is really there */ if (victim->d_inode && (victim->d_parent->d_inode == dir->d_inode)) { victim->d_inode->i_mtime = CURRENT_TIME; fsnotify_modify(victim); /** * Drop reference from initial sysfs_get_dentry(). */ dput(victim); res = 0; } else d_drop(victim); /** * Drop the reference acquired from sysfs_get_dentry() above. */ dput(victim); } mutex_unlock(&dir->d_inode->i_mutex);