![Arnd Bergmann](/assets/img/avatar_default.png)
All file_operations should get a .llseek operation so we can make nonseekable_open the default for future file operations without a .llseek pointer. The three cases that we can automatically detect are no_llseek, seq_lseek and default_llseek. For cases where we can we can automatically prove that the file offset is always ignored, we use noop_llseek, which maintains the current behavior of not returning an error from a seek. New drivers should normally not use noop_llseek but instead use no_llseek and call nonseekable_open at open time. Existing drivers can be converted to do the same when the maintainer knows for certain that no user code relies on calling seek on the device file. The generated code is often incorrectly indented and right now contains comments that clarify for each added line why a specific variant was chosen. In the version that gets submitted upstream, the comments will be gone and I will manually fix the indentation, because there does not seem to be a way to do that using coccinelle. Some amount of new code is currently sitting in linux-next that should get the same modifications, which I will do at the end of the merge window. Many thanks to Julia Lawall for helping me learn to write a semantic patch that does all this. ===== begin semantic patch ===== // This adds an llseek= method to all file operations, // as a preparation for making no_llseek the default. // // The rules are // - use no_llseek explicitly if we do nonseekable_open // - use seq_lseek for sequential files // - use default_llseek if we know we access f_pos // - use noop_llseek if we know we don't access f_pos, // but we still want to allow users to call lseek // @ open1 exists @ identifier nested_open; @@ nested_open(...) { <+... nonseekable_open(...) ...+> } @ open exists@ identifier open_f; identifier i, f; identifier open1.nested_open; @@ int open_f(struct inode *i, struct file *f) { <+... ( nonseekable_open(...) | nested_open(...) ) ...+> } @ read disable optional_qualifier exists @ identifier read_f; identifier f, p, s, off; type ssize_t, size_t, loff_t; expression E; identifier func; @@ ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off) { <+... ( *off = E | *off += E | func(..., off, ...) | E = *off ) ...+> } @ read_no_fpos disable optional_qualifier exists @ identifier read_f; identifier f, p, s, off; type ssize_t, size_t, loff_t; @@ ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off) { ... when != off } @ write @ identifier write_f; identifier f, p, s, off; type ssize_t, size_t, loff_t; expression E; identifier func; @@ ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off) { <+... ( *off = E | *off += E | func(..., off, ...) | E = *off ) ...+> } @ write_no_fpos @ identifier write_f; identifier f, p, s, off; type ssize_t, size_t, loff_t; @@ ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off) { ... when != off } @ fops0 @ identifier fops; @@ struct file_operations fops = { ... }; @ has_llseek depends on fops0 @ identifier fops0.fops; identifier llseek_f; @@ struct file_operations fops = { ... .llseek = llseek_f, ... }; @ has_read depends on fops0 @ identifier fops0.fops; identifier read_f; @@ struct file_operations fops = { ... .read = read_f, ... }; @ has_write depends on fops0 @ identifier fops0.fops; identifier write_f; @@ struct file_operations fops = { ... .write = write_f, ... }; @ has_open depends on fops0 @ identifier fops0.fops; identifier open_f; @@ struct file_operations fops = { ... .open = open_f, ... }; // use no_llseek if we call nonseekable_open //////////////////////////////////////////// @ nonseekable1 depends on !has_llseek && has_open @ identifier fops0.fops; identifier nso ~= "nonseekable_open"; @@ struct file_operations fops = { ... .open = nso, ... +.llseek = no_llseek, /* nonseekable */ }; @ nonseekable2 depends on !has_llseek @ identifier fops0.fops; identifier open.open_f; @@ struct file_operations fops = { ... .open = open_f, ... +.llseek = no_llseek, /* open uses nonseekable */ }; // use seq_lseek for sequential files ///////////////////////////////////// @ seq depends on !has_llseek @ identifier fops0.fops; identifier sr ~= "seq_read"; @@ struct file_operations fops = { ... .read = sr, ... +.llseek = seq_lseek, /* we have seq_read */ }; // use default_llseek if there is a readdir /////////////////////////////////////////// @ fops1 depends on !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; identifier readdir_e; @@ // any other fop is used that changes pos struct file_operations fops = { ... .readdir = readdir_e, ... +.llseek = default_llseek, /* readdir is present */ }; // use default_llseek if at least one of read/write touches f_pos ///////////////////////////////////////////////////////////////// @ fops2 depends on !fops1 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; identifier read.read_f; @@ // read fops use offset struct file_operations fops = { ... .read = read_f, ... +.llseek = default_llseek, /* read accesses f_pos */ }; @ fops3 depends on !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; identifier write.write_f; @@ // write fops use offset struct file_operations fops = { ... .write = write_f, ... + .llseek = default_llseek, /* write accesses f_pos */ }; // Use noop_llseek if neither read nor write accesses f_pos /////////////////////////////////////////////////////////// @ fops4 depends on !fops1 && !fops2 && !fops3 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; identifier read_no_fpos.read_f; identifier write_no_fpos.write_f; @@ // write fops use offset struct file_operations fops = { ... .write = write_f, .read = read_f, ... +.llseek = noop_llseek, /* read and write both use no f_pos */ }; @ depends on has_write && !has_read && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; identifier write_no_fpos.write_f; @@ struct file_operations fops = { ... .write = write_f, ... +.llseek = noop_llseek, /* write uses no f_pos */ }; @ depends on has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; identifier read_no_fpos.read_f; @@ struct file_operations fops = { ... .read = read_f, ... +.llseek = noop_llseek, /* read uses no f_pos */ }; @ depends on !has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @ identifier fops0.fops; @@ struct file_operations fops = { ... +.llseek = noop_llseek, /* no read or write fn */ }; ===== End semantic patch ===== Signed-off-by: Arnd Bergmann <arnd@arndb.de> Cc: Julia Lawall <julia@diku.dk> Cc: Christoph Hellwig <hch@infradead.org>
587 lines
14 KiB
C
587 lines
14 KiB
C
/*
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* linux/fs/char_dev.c
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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*/
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#include <linux/init.h>
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#include <linux/fs.h>
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#include <linux/kdev_t.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include <linux/major.h>
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#include <linux/errno.h>
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#include <linux/module.h>
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#include <linux/seq_file.h>
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#include <linux/kobject.h>
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#include <linux/kobj_map.h>
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#include <linux/cdev.h>
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#include <linux/mutex.h>
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#include <linux/backing-dev.h>
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#include <linux/tty.h>
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#include "internal.h"
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/*
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* capabilities for /dev/mem, /dev/kmem and similar directly mappable character
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* devices
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* - permits shared-mmap for read, write and/or exec
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* - does not permit private mmap in NOMMU mode (can't do COW)
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* - no readahead or I/O queue unplugging required
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*/
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struct backing_dev_info directly_mappable_cdev_bdi = {
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.name = "char",
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.capabilities = (
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#ifdef CONFIG_MMU
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/* permit private copies of the data to be taken */
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BDI_CAP_MAP_COPY |
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#endif
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/* permit direct mmap, for read, write or exec */
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BDI_CAP_MAP_DIRECT |
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BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP),
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};
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static struct kobj_map *cdev_map;
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static DEFINE_MUTEX(chrdevs_lock);
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static struct char_device_struct {
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struct char_device_struct *next;
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unsigned int major;
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unsigned int baseminor;
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int minorct;
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char name[64];
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struct cdev *cdev; /* will die */
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} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
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/* index in the above */
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static inline int major_to_index(int major)
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{
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return major % CHRDEV_MAJOR_HASH_SIZE;
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}
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#ifdef CONFIG_PROC_FS
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void chrdev_show(struct seq_file *f, off_t offset)
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{
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struct char_device_struct *cd;
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if (offset < CHRDEV_MAJOR_HASH_SIZE) {
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mutex_lock(&chrdevs_lock);
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for (cd = chrdevs[offset]; cd; cd = cd->next)
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seq_printf(f, "%3d %s\n", cd->major, cd->name);
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mutex_unlock(&chrdevs_lock);
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}
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}
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#endif /* CONFIG_PROC_FS */
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/*
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* Register a single major with a specified minor range.
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*
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* If major == 0 this functions will dynamically allocate a major and return
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* its number.
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*
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* If major > 0 this function will attempt to reserve the passed range of
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* minors and will return zero on success.
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*
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* Returns a -ve errno on failure.
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*/
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static struct char_device_struct *
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__register_chrdev_region(unsigned int major, unsigned int baseminor,
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int minorct, const char *name)
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{
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struct char_device_struct *cd, **cp;
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int ret = 0;
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int i;
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cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
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if (cd == NULL)
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return ERR_PTR(-ENOMEM);
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mutex_lock(&chrdevs_lock);
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/* temporary */
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if (major == 0) {
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for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
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if (chrdevs[i] == NULL)
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break;
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}
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if (i == 0) {
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ret = -EBUSY;
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goto out;
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}
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major = i;
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ret = major;
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}
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cd->major = major;
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cd->baseminor = baseminor;
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cd->minorct = minorct;
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strlcpy(cd->name, name, sizeof(cd->name));
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i = major_to_index(major);
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for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
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if ((*cp)->major > major ||
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((*cp)->major == major &&
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(((*cp)->baseminor >= baseminor) ||
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((*cp)->baseminor + (*cp)->minorct > baseminor))))
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break;
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/* Check for overlapping minor ranges. */
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if (*cp && (*cp)->major == major) {
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int old_min = (*cp)->baseminor;
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int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
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int new_min = baseminor;
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int new_max = baseminor + minorct - 1;
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/* New driver overlaps from the left. */
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if (new_max >= old_min && new_max <= old_max) {
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ret = -EBUSY;
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goto out;
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}
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/* New driver overlaps from the right. */
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if (new_min <= old_max && new_min >= old_min) {
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ret = -EBUSY;
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goto out;
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}
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}
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cd->next = *cp;
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*cp = cd;
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mutex_unlock(&chrdevs_lock);
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return cd;
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out:
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mutex_unlock(&chrdevs_lock);
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kfree(cd);
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return ERR_PTR(ret);
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}
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static struct char_device_struct *
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__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
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{
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struct char_device_struct *cd = NULL, **cp;
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int i = major_to_index(major);
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mutex_lock(&chrdevs_lock);
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for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
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if ((*cp)->major == major &&
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(*cp)->baseminor == baseminor &&
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(*cp)->minorct == minorct)
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break;
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if (*cp) {
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cd = *cp;
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*cp = cd->next;
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}
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mutex_unlock(&chrdevs_lock);
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return cd;
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}
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/**
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* register_chrdev_region() - register a range of device numbers
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* @from: the first in the desired range of device numbers; must include
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* the major number.
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* @count: the number of consecutive device numbers required
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* @name: the name of the device or driver.
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*
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* Return value is zero on success, a negative error code on failure.
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*/
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int register_chrdev_region(dev_t from, unsigned count, const char *name)
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{
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struct char_device_struct *cd;
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dev_t to = from + count;
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dev_t n, next;
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for (n = from; n < to; n = next) {
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next = MKDEV(MAJOR(n)+1, 0);
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if (next > to)
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next = to;
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cd = __register_chrdev_region(MAJOR(n), MINOR(n),
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next - n, name);
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if (IS_ERR(cd))
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goto fail;
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}
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return 0;
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fail:
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to = n;
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for (n = from; n < to; n = next) {
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next = MKDEV(MAJOR(n)+1, 0);
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kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
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}
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return PTR_ERR(cd);
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}
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/**
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* alloc_chrdev_region() - register a range of char device numbers
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* @dev: output parameter for first assigned number
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* @baseminor: first of the requested range of minor numbers
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* @count: the number of minor numbers required
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* @name: the name of the associated device or driver
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*
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* Allocates a range of char device numbers. The major number will be
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* chosen dynamically, and returned (along with the first minor number)
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* in @dev. Returns zero or a negative error code.
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*/
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int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
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const char *name)
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{
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struct char_device_struct *cd;
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cd = __register_chrdev_region(0, baseminor, count, name);
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if (IS_ERR(cd))
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return PTR_ERR(cd);
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*dev = MKDEV(cd->major, cd->baseminor);
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return 0;
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}
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/**
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* __register_chrdev() - create and register a cdev occupying a range of minors
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* @major: major device number or 0 for dynamic allocation
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* @baseminor: first of the requested range of minor numbers
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* @count: the number of minor numbers required
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* @name: name of this range of devices
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* @fops: file operations associated with this devices
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*
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* If @major == 0 this functions will dynamically allocate a major and return
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* its number.
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*
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* If @major > 0 this function will attempt to reserve a device with the given
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* major number and will return zero on success.
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*
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* Returns a -ve errno on failure.
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*
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* The name of this device has nothing to do with the name of the device in
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* /dev. It only helps to keep track of the different owners of devices. If
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* your module name has only one type of devices it's ok to use e.g. the name
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* of the module here.
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*/
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int __register_chrdev(unsigned int major, unsigned int baseminor,
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unsigned int count, const char *name,
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const struct file_operations *fops)
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{
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struct char_device_struct *cd;
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struct cdev *cdev;
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int err = -ENOMEM;
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cd = __register_chrdev_region(major, baseminor, count, name);
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if (IS_ERR(cd))
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return PTR_ERR(cd);
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cdev = cdev_alloc();
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if (!cdev)
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goto out2;
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cdev->owner = fops->owner;
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cdev->ops = fops;
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kobject_set_name(&cdev->kobj, "%s", name);
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err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
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if (err)
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goto out;
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cd->cdev = cdev;
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return major ? 0 : cd->major;
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out:
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kobject_put(&cdev->kobj);
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out2:
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kfree(__unregister_chrdev_region(cd->major, baseminor, count));
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return err;
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}
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/**
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* unregister_chrdev_region() - return a range of device numbers
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* @from: the first in the range of numbers to unregister
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* @count: the number of device numbers to unregister
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*
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* This function will unregister a range of @count device numbers,
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* starting with @from. The caller should normally be the one who
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* allocated those numbers in the first place...
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*/
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void unregister_chrdev_region(dev_t from, unsigned count)
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{
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dev_t to = from + count;
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dev_t n, next;
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for (n = from; n < to; n = next) {
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next = MKDEV(MAJOR(n)+1, 0);
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if (next > to)
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next = to;
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kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
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}
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}
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/**
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* __unregister_chrdev - unregister and destroy a cdev
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* @major: major device number
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* @baseminor: first of the range of minor numbers
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* @count: the number of minor numbers this cdev is occupying
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* @name: name of this range of devices
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*
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* Unregister and destroy the cdev occupying the region described by
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* @major, @baseminor and @count. This function undoes what
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* __register_chrdev() did.
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*/
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void __unregister_chrdev(unsigned int major, unsigned int baseminor,
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unsigned int count, const char *name)
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{
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struct char_device_struct *cd;
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cd = __unregister_chrdev_region(major, baseminor, count);
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if (cd && cd->cdev)
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cdev_del(cd->cdev);
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kfree(cd);
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}
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static DEFINE_SPINLOCK(cdev_lock);
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static struct kobject *cdev_get(struct cdev *p)
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{
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struct module *owner = p->owner;
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struct kobject *kobj;
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if (owner && !try_module_get(owner))
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return NULL;
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kobj = kobject_get(&p->kobj);
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if (!kobj)
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module_put(owner);
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return kobj;
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}
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void cdev_put(struct cdev *p)
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{
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if (p) {
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struct module *owner = p->owner;
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kobject_put(&p->kobj);
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module_put(owner);
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}
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}
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/*
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* Called every time a character special file is opened
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*/
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static int chrdev_open(struct inode *inode, struct file *filp)
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{
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struct cdev *p;
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struct cdev *new = NULL;
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int ret = 0;
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spin_lock(&cdev_lock);
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p = inode->i_cdev;
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if (!p) {
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struct kobject *kobj;
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int idx;
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spin_unlock(&cdev_lock);
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kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
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if (!kobj)
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return -ENXIO;
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new = container_of(kobj, struct cdev, kobj);
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spin_lock(&cdev_lock);
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/* Check i_cdev again in case somebody beat us to it while
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we dropped the lock. */
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p = inode->i_cdev;
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if (!p) {
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inode->i_cdev = p = new;
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list_add(&inode->i_devices, &p->list);
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new = NULL;
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} else if (!cdev_get(p))
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ret = -ENXIO;
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} else if (!cdev_get(p))
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ret = -ENXIO;
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spin_unlock(&cdev_lock);
|
|
cdev_put(new);
|
|
if (ret)
|
|
return ret;
|
|
|
|
ret = -ENXIO;
|
|
filp->f_op = fops_get(p->ops);
|
|
if (!filp->f_op)
|
|
goto out_cdev_put;
|
|
|
|
if (filp->f_op->open) {
|
|
ret = filp->f_op->open(inode,filp);
|
|
if (ret)
|
|
goto out_cdev_put;
|
|
}
|
|
|
|
return 0;
|
|
|
|
out_cdev_put:
|
|
cdev_put(p);
|
|
return ret;
|
|
}
|
|
|
|
int cdev_index(struct inode *inode)
|
|
{
|
|
int idx;
|
|
struct kobject *kobj;
|
|
|
|
kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
|
|
if (!kobj)
|
|
return -1;
|
|
kobject_put(kobj);
|
|
return idx;
|
|
}
|
|
|
|
void cd_forget(struct inode *inode)
|
|
{
|
|
spin_lock(&cdev_lock);
|
|
list_del_init(&inode->i_devices);
|
|
inode->i_cdev = NULL;
|
|
spin_unlock(&cdev_lock);
|
|
}
|
|
|
|
static void cdev_purge(struct cdev *cdev)
|
|
{
|
|
spin_lock(&cdev_lock);
|
|
while (!list_empty(&cdev->list)) {
|
|
struct inode *inode;
|
|
inode = container_of(cdev->list.next, struct inode, i_devices);
|
|
list_del_init(&inode->i_devices);
|
|
inode->i_cdev = NULL;
|
|
}
|
|
spin_unlock(&cdev_lock);
|
|
}
|
|
|
|
/*
|
|
* Dummy default file-operations: the only thing this does
|
|
* is contain the open that then fills in the correct operations
|
|
* depending on the special file...
|
|
*/
|
|
const struct file_operations def_chr_fops = {
|
|
.open = chrdev_open,
|
|
.llseek = noop_llseek,
|
|
};
|
|
|
|
static struct kobject *exact_match(dev_t dev, int *part, void *data)
|
|
{
|
|
struct cdev *p = data;
|
|
return &p->kobj;
|
|
}
|
|
|
|
static int exact_lock(dev_t dev, void *data)
|
|
{
|
|
struct cdev *p = data;
|
|
return cdev_get(p) ? 0 : -1;
|
|
}
|
|
|
|
/**
|
|
* cdev_add() - add a char device to the system
|
|
* @p: the cdev structure for the device
|
|
* @dev: the first device number for which this device is responsible
|
|
* @count: the number of consecutive minor numbers corresponding to this
|
|
* device
|
|
*
|
|
* cdev_add() adds the device represented by @p to the system, making it
|
|
* live immediately. A negative error code is returned on failure.
|
|
*/
|
|
int cdev_add(struct cdev *p, dev_t dev, unsigned count)
|
|
{
|
|
p->dev = dev;
|
|
p->count = count;
|
|
return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
|
|
}
|
|
|
|
static void cdev_unmap(dev_t dev, unsigned count)
|
|
{
|
|
kobj_unmap(cdev_map, dev, count);
|
|
}
|
|
|
|
/**
|
|
* cdev_del() - remove a cdev from the system
|
|
* @p: the cdev structure to be removed
|
|
*
|
|
* cdev_del() removes @p from the system, possibly freeing the structure
|
|
* itself.
|
|
*/
|
|
void cdev_del(struct cdev *p)
|
|
{
|
|
cdev_unmap(p->dev, p->count);
|
|
kobject_put(&p->kobj);
|
|
}
|
|
|
|
|
|
static void cdev_default_release(struct kobject *kobj)
|
|
{
|
|
struct cdev *p = container_of(kobj, struct cdev, kobj);
|
|
cdev_purge(p);
|
|
}
|
|
|
|
static void cdev_dynamic_release(struct kobject *kobj)
|
|
{
|
|
struct cdev *p = container_of(kobj, struct cdev, kobj);
|
|
cdev_purge(p);
|
|
kfree(p);
|
|
}
|
|
|
|
static struct kobj_type ktype_cdev_default = {
|
|
.release = cdev_default_release,
|
|
};
|
|
|
|
static struct kobj_type ktype_cdev_dynamic = {
|
|
.release = cdev_dynamic_release,
|
|
};
|
|
|
|
/**
|
|
* cdev_alloc() - allocate a cdev structure
|
|
*
|
|
* Allocates and returns a cdev structure, or NULL on failure.
|
|
*/
|
|
struct cdev *cdev_alloc(void)
|
|
{
|
|
struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
|
|
if (p) {
|
|
INIT_LIST_HEAD(&p->list);
|
|
kobject_init(&p->kobj, &ktype_cdev_dynamic);
|
|
}
|
|
return p;
|
|
}
|
|
|
|
/**
|
|
* cdev_init() - initialize a cdev structure
|
|
* @cdev: the structure to initialize
|
|
* @fops: the file_operations for this device
|
|
*
|
|
* Initializes @cdev, remembering @fops, making it ready to add to the
|
|
* system with cdev_add().
|
|
*/
|
|
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
|
|
{
|
|
memset(cdev, 0, sizeof *cdev);
|
|
INIT_LIST_HEAD(&cdev->list);
|
|
kobject_init(&cdev->kobj, &ktype_cdev_default);
|
|
cdev->ops = fops;
|
|
}
|
|
|
|
static struct kobject *base_probe(dev_t dev, int *part, void *data)
|
|
{
|
|
if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
|
|
/* Make old-style 2.4 aliases work */
|
|
request_module("char-major-%d", MAJOR(dev));
|
|
return NULL;
|
|
}
|
|
|
|
void __init chrdev_init(void)
|
|
{
|
|
cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
|
|
bdi_init(&directly_mappable_cdev_bdi);
|
|
}
|
|
|
|
|
|
/* Let modules do char dev stuff */
|
|
EXPORT_SYMBOL(register_chrdev_region);
|
|
EXPORT_SYMBOL(unregister_chrdev_region);
|
|
EXPORT_SYMBOL(alloc_chrdev_region);
|
|
EXPORT_SYMBOL(cdev_init);
|
|
EXPORT_SYMBOL(cdev_alloc);
|
|
EXPORT_SYMBOL(cdev_del);
|
|
EXPORT_SYMBOL(cdev_add);
|
|
EXPORT_SYMBOL(cdev_index);
|
|
EXPORT_SYMBOL(__register_chrdev);
|
|
EXPORT_SYMBOL(__unregister_chrdev);
|
|
EXPORT_SYMBOL(directly_mappable_cdev_bdi);
|