/* * fs/sysfs/file.c - sysfs regular (text) file implementation * * Copyright (c) 2001-3 Patrick Mochel * Copyright (c) 2007 SUSE Linux Products GmbH * Copyright (c) 2007 Tejun Heo <teheo@suse.de> * * This file is released under the GPLv2. * * Please see Documentation/filesystems/sysfs.txt for more information. */ #include <linux/module.h>#include <linux/kobject.h>#include <linux/kallsyms.h>#include <linux/slab.h>#include <linux/fsnotify.h>#include <linux/namei.h>#include <linux/poll.h>#include <linux/list.h>#include <linux/mutex.h>#include <linux/limits.h>#include <asm/uaccess.h> #include "sysfs.h" /* * There's one sysfs_buffer for each open file and one * sysfs_open_dirent for each sysfs_dirent with one or more open * files. * * filp->private_data points to sysfs_buffer and * sysfs_dirent->s_attr.open points to sysfs_open_dirent. s_attr.open * is protected by sysfs_open_dirent_lock. */static DEFINE_SPINLOCK(sysfs_open_dirent_lock); struct sysfs_open_dirent { atomic_t refcnt; atomic_t event; wait_queue_head_t poll; struct list_head buffers; /* goes through sysfs_buffer.list */}; struct sysfs_buffer { size_t count; loff_t pos; char * page; const struct sysfs_ops * ops; struct mutex mutex; int needs_read_fill; int event; struct list_head list;}; /** * 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 unless an error * is returned. */static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer){ struct sysfs_dirent *attr_sd = dentry->d_fsdata; struct kobject *kobj = attr_sd->s_parent->s_dir.kobj; const 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; /* need attr_sd for attr and ops, its parent for kobj */ if (!sysfs_get_active(attr_sd)) return -ENODEV; buffer->event = atomic_read(&attr_sd->s_attr.open->event); count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page); sysfs_put_active(attr_sd); /* * The code works fine with PAGE_SIZE return but it's likely to * indicate truncated result or overflow in normal use cases. */ if (count >= (ssize_t)PAGE_SIZE) { print_symbol("fill_read_buffer: %s returned bad count\n", (unsigned long)ops->show); /* Try to struggle along */ count = PAGE_SIZE - 1; } if (count >= 0) { buffer->needs_read_fill = 0; buffer->count = count; } else { ret = count; } return ret;} /** * 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; mutex_lock(&buffer->mutex); if (buffer->needs_read_fill || *ppos == 0) { retval = fill_read_buffer(file->f_path.dentry,buffer); if (retval) goto out; } pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n", __func__, count, *ppos, buffer->page); retval = simple_read_from_buffer(buf, count, ppos, buffer->page, buffer->count);out: mutex_unlock(&buffer->mutex); 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; /* if buf is assumed to contain a string, terminate it by \0, so e.g. sscanf() can scan the string easily */ buffer->page[count] = 0; 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 intflush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count){ struct sysfs_dirent *attr_sd = dentry->d_fsdata; struct kobject *kobj = attr_sd->s_parent->s_dir.kobj; const struct sysfs_ops * ops = buffer->ops; int rc; /* need attr_sd for attr and ops, its parent for kobj */ if (!sysfs_get_active(attr_sd)) return -ENODEV; rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count); sysfs_put_active(attr_sd); return rc;} /** * 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; mutex_lock(&buffer->mutex); len = fill_write_buffer(buffer, buf, count); if (len > 0) len = flush_write_buffer(file->f_path.dentry, buffer, len); if (len > 0) *ppos += len; mutex_unlock(&buffer->mutex); return len;} /** * sysfs_get_open_dirent - get or create sysfs_open_dirent * @sd: target sysfs_dirent * @buffer: sysfs_buffer for this instance of open * * If @sd->s_attr.open exists, increment its reference count; * otherwise, create one. @buffer is chained to the buffers * list. * * LOCKING: * Kernel thread context (may sleep). * * RETURNS: * 0 on success, -errno on failure. */static int sysfs_get_open_dirent(struct sysfs_dirent *sd, struct sysfs_buffer *buffer){ struct sysfs_open_dirent *od, *new_od = NULL; retry: spin_lock_irq(&sysfs_open_dirent_lock); if (!sd->s_attr.open && new_od) { sd->s_attr.open = new_od; new_od = NULL; } od = sd->s_attr.open; if (od) { atomic_inc(&od->refcnt); list_add_tail(&buffer->list, &od->buffers); } spin_unlock_irq(&sysfs_open_dirent_lock); if (od) { kfree(new_od); return 0; } /* not there, initialize a new one and retry */ new_od = kmalloc(sizeof(*new_od), GFP_KERNEL); if (!new_od) return -ENOMEM; atomic_set(&new_od->refcnt, 0); atomic_set(&new_od->event, 1); init_waitqueue_head(&new_od->poll); INIT_LIST_HEAD(&new_od->buffers); goto retry;} /** * sysfs_put_open_dirent - put sysfs_open_dirent * @sd: target sysfs_dirent * @buffer: associated sysfs_buffer * * Put @sd->s_attr.open and unlink @buffer from the buffers list. * If reference count reaches zero, disassociate and free it. * * LOCKING: * None. */static void sysfs_put_open_dirent(struct sysfs_dirent *sd, struct sysfs_buffer *buffer){ struct sysfs_open_dirent *od = sd->s_attr.open; unsigned long flags; spin_lock_irqsave(&sysfs_open_dirent_lock, flags); list_del(&buffer->list); if (atomic_dec_and_test(&od->refcnt)) sd->s_attr.open = NULL; else od = NULL; spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags); kfree(od);} static int sysfs_open_file(struct inode *inode, struct file *file){ struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata; struct kobject *kobj = attr_sd->s_parent->s_dir.kobj; struct sysfs_buffer *buffer; const struct sysfs_ops *ops; int error = -EACCES; /* need attr_sd for attr and ops, its parent for kobj */ if (!sysfs_get_active(attr_sd)) return -ENODEV; /* every kobject with an attribute needs a ktype assigned */ if (kobj->ktype && kobj->ktype->sysfs_ops) ops = kobj->ktype->sysfs_ops; else { WARN(1, KERN_ERR "missing sysfs attribute operations for " "kobject: %s\n", kobject_name(kobj)); goto err_out; } /* 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 err_out; } /* 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 err_out; } /* No error? Great, allocate a buffer for the file, and store it * it in file->private_data for easy access. */ error = -ENOMEM; buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL); if (!buffer) goto err_out; mutex_init(&buffer->mutex); buffer->needs_read_fill = 1; buffer->ops = ops; file->private_data = buffer; /* make sure we have open dirent struct */ error = sysfs_get_open_dirent(attr_sd, buffer); if (error) goto err_free; /* open succeeded, put active references */ sysfs_put_active(attr_sd); return 0; err_free: kfree(buffer); err_out: sysfs_put_active(attr_sd); return error;} static int sysfs_release(struct inode *inode, struct file *filp){ struct sysfs_dirent *sd = filp->f_path.dentry->d_fsdata; struct sysfs_buffer *buffer = filp->private_data; sysfs_put_open_dirent(sd, 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, or seek to 0 and read again. * 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 (Neither 'poll' nor '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 sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata; struct sysfs_open_dirent *od = attr_sd->s_attr.open; /* need parent for the kobj, grab both */ if (!sysfs_get_active(attr_sd)) goto trigger; poll_wait(filp, &od->poll, wait); sysfs_put_active(attr_sd); if (buffer->event != atomic_read(&od->event)) goto trigger; return DEFAULT_POLLMASK; trigger: buffer->needs_read_fill = 1; return DEFAULT_POLLMASK|POLLERR|POLLPRI;} void sysfs_notify_dirent(struct sysfs_dirent *sd){ struct sysfs_open_dirent *od; unsigned long flags; spin_lock_irqsave(&sysfs_open_dirent_lock, flags); od = sd->s_attr.open; if (od) { atomic_inc(&od->event); wake_up_interruptible(&od->poll); } spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags);}EXPORT_SYMBOL_GPL(sysfs_notify_dirent); void sysfs_notify(struct kobject *k, const char *dir, const char *attr){ struct sysfs_dirent *sd = k->sd; mutex_lock(&sysfs_mutex); if (sd && dir) sd = sysfs_find_dirent(sd, NULL, dir); if (sd && attr) sd = sysfs_find_dirent(sd, NULL, attr); if (sd) sysfs_notify_dirent(sd); mutex_unlock(&sysfs_mutex);}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_attr_ns(struct kobject *kobj, const struct attribute *attr, const void **pns){ struct sysfs_dirent *dir_sd = kobj->sd; const struct sysfs_ops *ops; const void *ns = NULL; int err; if (!dir_sd) { WARN(1, KERN_ERR "sysfs: kobject %s without dirent\n", kobject_name(kobj)); return -ENOENT; }Lines 1–500 of 799. 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/* * fs/sysfs/file.c - sysfs regular (text) file implementation * * Copyright (c) 2001-3 Patrick Mochel * Copyright (c) 2007 SUSE Linux Products GmbH * Copyright (c) 2007 Tejun Heo <teheo@suse.de> * * This file is released under the GPLv2. * * Please see Documentation/filesystems/sysfs.txt for more information. */ #include <linux/module.h> #include <linux/kobject.h> #include <linux/kallsyms.h> #include <linux/slab.h> #include <linux/fsnotify.h> #include <linux/namei.h> #include <linux/poll.h> #include <linux/list.h> #include <linux/mutex.h> #include <linux/limits.h> #include <asm/uaccess.h> #include "sysfs.h" /* * There's one sysfs_buffer for each open file and one * sysfs_open_dirent for each sysfs_dirent with one or more open * files. * * filp->private_data points to sysfs_buffer and * sysfs_dirent->s_attr.open points to sysfs_open_dirent. s_attr.open * is protected by sysfs_open_dirent_lock. */ static DEFINE_SPINLOCK(sysfs_open_dirent_lock); struct sysfs_open_dirent { atomic_t refcnt; atomic_t event; wait_queue_head_t poll; struct list_head buffers; /* goes through sysfs_buffer.list */ }; struct sysfs_buffer { size_t count; loff_t pos; char * page; const struct sysfs_ops * ops; struct mutex mutex; int needs_read_fill; int event; struct list_head list; }; /** * 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 unless an error * is returned. */ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer) { struct sysfs_dirent *attr_sd = dentry->d_fsdata; struct kobject *kobj = attr_sd->s_parent->s_dir.kobj; const 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; /* need attr_sd for attr and ops, its parent for kobj */ if (!sysfs_get_active(attr_sd)) return -ENODEV; buffer->event = atomic_read(&attr_sd->s_attr.open->event); count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page); sysfs_put_active(attr_sd); /* * The code works fine with PAGE_SIZE return but it's likely to * indicate truncated result or overflow in normal use cases. */ if (count >= (ssize_t)PAGE_SIZE) { print_symbol("fill_read_buffer: %s returned bad count\n", (unsigned long)ops->show); /* Try to struggle along */ count = PAGE_SIZE - 1; } if (count >= 0) { buffer->needs_read_fill = 0; buffer->count = count; } else { ret = count; } return ret; } /** * 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; mutex_lock(&buffer->mutex); if (buffer->needs_read_fill || *ppos == 0) { retval = fill_read_buffer(file->f_path.dentry,buffer); if (retval) goto out; } pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n", __func__, count, *ppos, buffer->page); retval = simple_read_from_buffer(buf, count, ppos, buffer->page, buffer->count); out: mutex_unlock(&buffer->mutex); 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; /* if buf is assumed to contain a string, terminate it by \0, so e.g. sscanf() can scan the string easily */ buffer->page[count] = 0; 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 sysfs_dirent *attr_sd = dentry->d_fsdata; struct kobject *kobj = attr_sd->s_parent->s_dir.kobj; const struct sysfs_ops * ops = buffer->ops; int rc; /* need attr_sd for attr and ops, its parent for kobj */ if (!sysfs_get_active(attr_sd)) return -ENODEV; rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count); sysfs_put_active(attr_sd); return rc; } /** * 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; mutex_lock(&buffer->mutex); len = fill_write_buffer(buffer, buf, count); if (len > 0) len = flush_write_buffer(file->f_path.dentry, buffer, len); if (len > 0) *ppos += len; mutex_unlock(&buffer->mutex); return len; } /** * sysfs_get_open_dirent - get or create sysfs_open_dirent * @sd: target sysfs_dirent * @buffer: sysfs_buffer for this instance of open * * If @sd->s_attr.open exists, increment its reference count; * otherwise, create one. @buffer is chained to the buffers * list. * * LOCKING: * Kernel thread context (may sleep). * * RETURNS: * 0 on success, -errno on failure. */ static int sysfs_get_open_dirent(struct sysfs_dirent *sd, struct sysfs_buffer *buffer) { struct sysfs_open_dirent *od, *new_od = NULL; retry: spin_lock_irq(&sysfs_open_dirent_lock); if (!sd->s_attr.open && new_od) { sd->s_attr.open = new_od; new_od = NULL; } od = sd->s_attr.open; if (od) { atomic_inc(&od->refcnt); list_add_tail(&buffer->list, &od->buffers); } spin_unlock_irq(&sysfs_open_dirent_lock); if (od) { kfree(new_od); return 0; } /* not there, initialize a new one and retry */ new_od = kmalloc(sizeof(*new_od), GFP_KERNEL); if (!new_od) return -ENOMEM; atomic_set(&new_od->refcnt, 0); atomic_set(&new_od->event, 1); init_waitqueue_head(&new_od->poll); INIT_LIST_HEAD(&new_od->buffers); goto retry; } /** * sysfs_put_open_dirent - put sysfs_open_dirent * @sd: target sysfs_dirent * @buffer: associated sysfs_buffer * * Put @sd->s_attr.open and unlink @buffer from the buffers list. * If reference count reaches zero, disassociate and free it. * * LOCKING: * None. */ static void sysfs_put_open_dirent(struct sysfs_dirent *sd, struct sysfs_buffer *buffer) { struct sysfs_open_dirent *od = sd->s_attr.open; unsigned long flags; spin_lock_irqsave(&sysfs_open_dirent_lock, flags); list_del(&buffer->list); if (atomic_dec_and_test(&od->refcnt)) sd->s_attr.open = NULL; else od = NULL; spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags); kfree(od); } static int sysfs_open_file(struct inode *inode, struct file *file) { struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata; struct kobject *kobj = attr_sd->s_parent->s_dir.kobj; struct sysfs_buffer *buffer; const struct sysfs_ops *ops; int error = -EACCES; /* need attr_sd for attr and ops, its parent for kobj */ if (!sysfs_get_active(attr_sd)) return -ENODEV; /* every kobject with an attribute needs a ktype assigned */ if (kobj->ktype && kobj->ktype->sysfs_ops) ops = kobj->ktype->sysfs_ops; else { WARN(1, KERN_ERR "missing sysfs attribute operations for " "kobject: %s\n", kobject_name(kobj)); goto err_out; } /* 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 err_out; } /* 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 err_out; } /* No error? Great, allocate a buffer for the file, and store it * it in file->private_data for easy access. */ error = -ENOMEM; buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL); if (!buffer) goto err_out; mutex_init(&buffer->mutex); buffer->needs_read_fill = 1; buffer->ops = ops; file->private_data = buffer; /* make sure we have open dirent struct */ error = sysfs_get_open_dirent(attr_sd, buffer); if (error) goto err_free; /* open succeeded, put active references */ sysfs_put_active(attr_sd); return 0; err_free: kfree(buffer); err_out: sysfs_put_active(attr_sd); return error; } static int sysfs_release(struct inode *inode, struct file *filp) { struct sysfs_dirent *sd = filp->f_path.dentry->d_fsdata; struct sysfs_buffer *buffer = filp->private_data; sysfs_put_open_dirent(sd, 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, or seek to 0 and read again. * 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 (Neither 'poll' nor '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 sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata; struct sysfs_open_dirent *od = attr_sd->s_attr.open; /* need parent for the kobj, grab both */ if (!sysfs_get_active(attr_sd)) goto trigger; poll_wait(filp, &od->poll, wait); sysfs_put_active(attr_sd); if (buffer->event != atomic_read(&od->event)) goto trigger; return DEFAULT_POLLMASK; trigger: buffer->needs_read_fill = 1; return DEFAULT_POLLMASK|POLLERR|POLLPRI; } void sysfs_notify_dirent(struct sysfs_dirent *sd) { struct sysfs_open_dirent *od; unsigned long flags; spin_lock_irqsave(&sysfs_open_dirent_lock, flags); od = sd->s_attr.open; if (od) { atomic_inc(&od->event); wake_up_interruptible(&od->poll); } spin_unlock_irqrestore(&sysfs_open_dirent_lock, flags); } EXPORT_SYMBOL_GPL(sysfs_notify_dirent); void sysfs_notify(struct kobject *k, const char *dir, const char *attr) { struct sysfs_dirent *sd = k->sd; mutex_lock(&sysfs_mutex); if (sd && dir) sd = sysfs_find_dirent(sd, NULL, dir); if (sd && attr) sd = sysfs_find_dirent(sd, NULL, attr); if (sd) sysfs_notify_dirent(sd); mutex_unlock(&sysfs_mutex); } 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_attr_ns(struct kobject *kobj, const struct attribute *attr, const void **pns) { struct sysfs_dirent *dir_sd = kobj->sd; const struct sysfs_ops *ops; const void *ns = NULL; int err; if (!dir_sd) { WARN(1, KERN_ERR "sysfs: kobject %s without dirent\n", kobject_name(kobj)); return -ENOENT; }