The program code
lwfs ==> superblock operations, registering the file system and unregistering the file system code.
file.c ==> file_operations implementation.
inode.c ==> inode_operations implementation.
Problem which I am facing with this code ==>
After mounting the file system. When I do echo "test" > mnt_pt/some_file_name. It is giving oops. When file is getting closed.
Here, are some of the messages displayed in the dmesg
[ 4950.360171] Got good INODE.
[ 4950.360191] Got good INODE.
[ 4950.360205] Got good INODE.
[ 4950.360217] Got good INODE.
[ 4960.322256] Got good INODE.
[ 4960.322267] Inode Created : 17190 = test<1>BUG: unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 4960.322328] printing eip:
[ 4960.322332] c01f3ffe
[ 4960.322335] *pde = 00000000
[ 4960.322341] Oops: 0000 [#2]
[ 4960.322344] SMP
[ 4960.322350] Modules linked in: fs cpufreq_stats cpufreq_ondemand freq_table ac evdev thermal processor fan
[ 4960.322370] CPU: 1
[ 4960.322372] EIP: 0060:[<c01f3ffe>] Not tainted VLI
[ 4960.322376] EFLAGS: 00010282 (2.6.20 #8)
[ 4960.322386] EIP is at list_del+0xa/0x61
[ 4960.322391] eax: f8868080 ebx: f8868044 ecx: 00000000 edx: e75ef5cc
[ 4960.322398] esi: f8868080 edi: 00000000 ebp: e9464f30 esp: e9464f20
[ 4960.322403] ds: 007b es: 007b ss: 0068
[ 4960.322409] Process bash (pid: 6062, ti=e9464000 task=f751b4f0 task.ti=e9464000)
[ 4960.322415] Stack: e75ef5cc e9464f30 c0344186 f8868044 e9464f48 c0179342 e75ef5cc 00000008
[ 4960.322430] f599e03c e75ef5cc e9464f70 c0155b0a 00000000 00000000 e826b1cc dfff0988
[ 4960.322445] f599e03c e75ef5cc f7baaca8 00000000 e9464f78 c0155bd8 e9464f90 c0153610
[ 4960.322459] Call Trace:
[ 4960.322462] [<c01048a2>] show_trace_log_lvl+0x1a/0x2f
[ 4960.322472] [<c0104954>] show_stack_log_lvl+0x9d/0xa5
[ 4960.322481] [<c0104af1>] show_registers+0x195/0x26b
[ 4960.322489] [<c0104ce0>] die+0x119/0x21a
[ 4960.322496] [<c034713d>] do_page_fault+0x443/0x514
[ 4960.322504] [<c034597c>] error_code+0x7c/0x84
[ 4960.322511] [<c0179342>] eventpoll_release_file+0x25/0x69
[ 4960.322519] [<c0155b0a>] __fput+0xa3/0x15a
[ 4960.322526] [<c0155bd8>] fput+0x17/0x19
[ 4960.322532] [<c0153610>] filp_close+0x54/0x5c
[ 4960.322539] [<c015e6e9>] sys_dup2+0xd0/0xfc
[ 4960.322547] [<c0103854>] sysenter_past_esp+0x5d/0x99
[ 4960.322555] =======================
[ 4960.322558] Code: 00 00 8d 4b 0c 8b 51 04 8d 46 0c e8 72 00 00 00 89 f8 e8 87 fe ff ff 83 c4 10 5b 5e 5f 5d c3 90 90 55 89 e5 53 83 ec 0c 8b 48 04 <8b> 11 39 c2 74 18 89 54 24 08 89 44 24 04 c7 04 24 92 37 3e c0
[ 4960.322635] EIP: [<c01f3ffe>] list_del+0xa/0x61 SS:ESP 0068:e9464f20
Please help........
Thanks and Regards,
Prasad.
Code is as follows.
root@prasad-desktop:/home/prasad/programs/ldd/lwfs# cat lwfs.c
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/pagemap.h> /* PAGE_CACHE_SIZE */
#include <linux/fs.h> /* This is where libfs stuff is declared */
#include <asm/atomic.h>
#include <asm/uaccess.h> /* copy_to_user */
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Jonathan Corbet");
#define LFS_MAGIC 0x19980122
#include "file.h"
#include "inode.h"
static struct dentry *lfs_create_dir (struct super_block *sb, struct dentry *parent, const char *name)
{
struct dentry *dentry;
struct inode *inode;
struct qstr qname;
qname.name = name;
qname.len = strlen (name);
qname.hash = full_name_hash(name, qname.len);
dentry = d_alloc(parent, &qname);
if (! dentry)
goto out;
inode = lfs_make_inode(sb, S_IFDIR | 0777);
if (! inode)
goto out_dput;
inode->i_op = &lwfs_i_ops;
inode->i_fop = &simple_dir_operations;
d_add(dentry, inode);
return dentry;
out_dput:
dput(dentry);
out:
return 0;
}
static void lfs_create_files (struct super_block *sb, struct dentry *root)
{
struct dentry *subdir;
atomic_set(&counter, 0);
lfs_create_file(sb, root, "counter", &counter);
atomic_set(&subcounter, 0);
subdir = lfs_create_dir(sb, root, "subdir");
if (subdir)
lfs_create_file(sb, subdir, "subcounter", &subcounter);
}
static struct super_operations lfs_s_ops =
{
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
};
static int lfs_fill_super (struct super_block *sb, void *data, int silent)
{
struct inode *root;
struct dentry *root_dentry;
sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = LFS_MAGIC;
sb->s_op = &lfs_s_ops;
root = lfs_make_inode (sb, S_IFDIR | 0777);
if (! root)
goto out;
root->i_op = &lwfs_i_ops;
root->i_fop = &simple_dir_operations;
root_dentry = d_alloc_root(root);
if (! root_dentry)
goto out_iput;
sb->s_root = root_dentry;
lfs_create_files (sb, root_dentry);
return 0;
out_iput:
iput(root);
out:
return -ENOMEM;
}
static int lfs_get_super(struct file_system_type *fst, int flags, const char *devname, void *data, struct vfsmount *mnt )
{
return get_sb_single(fst, flags, data, lfs_fill_super, mnt);
}
static struct file_system_type lfs_type = {
.owner = THIS_MODULE,
.name = "lwnfs",
.get_sb = lfs_get_super,
.kill_sb = kill_litter_super,
};
static int __init lfs_init(void)
{
return register_filesystem(&lfs_type);
}
static void __exit lfs_exit(void)
{
unregister_filesystem(&lfs_type);
}
module_init(lfs_init);
module_exit(lfs_exit);
root@prasad-desktop:/home/prasad/programs/ldd/lwfs# cat file.c
#include <linux/fs.h>
#include <asm/uaccess.h>
#include "file.h"
#include "inode.h"
#define TMPSIZE 20
struct file_operations lfs_file_ops =
{
.open = lfs_open,
.read = lfs_read_file,
.write = lfs_write_file,
};
int lfs_open(struct inode *inode, struct file *filp)
{
filp->private_data = inode->i_private;
return 0;
}
ssize_t lfs_read_file(struct file *filp, char *buf, size_t count, loff_t *offset)
{
atomic_t *counter = (atomic_t *) filp->private_data;
int v, len;
char tmp[TMPSIZE];
v = atomic_read(counter);
if (*offset > 0)
v -= 1; /* the value returned when offset was zero */
else
atomic_inc(counter);
len = snprintf(tmp, TMPSIZE, "%d\n", v);
if (*offset > len)
return 0;
if (count > len - *offset)
count = len - *offset;
if (copy_to_user(buf, tmp + *offset, count))
return -EFAULT;
*offset += count;
return count;
}
ssize_t lfs_write_file(struct file *filp, const char *buf, size_t count, loff_t *offset)
{
atomic_t *counter = (atomic_t *) filp->private_data;
char tmp[TMPSIZE];
if (*offset != 0)
return -EINVAL;
if (count >= TMPSIZE)
return -EINVAL;
memset(tmp, 0, TMPSIZE);
if (copy_from_user(tmp, buf, count))
return -EFAULT;
atomic_set(counter, simple_strtol(tmp, NULL, 10));
return count;
}
struct dentry *lfs_create_file (struct super_block *sb, struct dentry *dir, const char *name, atomic_t *counter)
{
struct dentry *dentry;
struct inode *inode;
struct qstr qname;
qname.name = name;
qname.len = strlen (name);
qname.hash = full_name_hash(name, qname.len);
dentry = d_alloc(dir, &qname);
if (! dentry)
goto out;
inode = lfs_make_inode(sb, S_IFREG | 777);
if (! inode)
goto out_dput;
inode->i_fop = &lfs_file_ops;
inode->i_private = counter;
d_add(dentry, inode);
return dentry;
out_dput:
dput(dentry);
out:
return 0;
}
root@prasad-desktop:/home/prasad/programs/ldd/lwfs# cat inode.c
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <asm/atomic.h>
#include "inode.h"
#include "file.h"
atomic_t counter, subcounter ;
struct inode_operations lwfs_i_ops =
{
.lookup = simple_lookup,
.create = create_inode,
.unlink = unlink_inode
} ;
int unlink_inode (struct inode *dir,struct dentry *dentry)
{
struct inode *inode = dentry->d_inode;
inode_dec_link_count(inode);
return 0 ;
}
int create_inode (struct inode * dir, struct dentry *dentry, int mode, struct nameidata *nd )
{
struct inode *inode = lfs_make_inode ( dir->i_sb, mode) ;
if ( !inode )
goto out;
inode->i_fop = &lfs_file_ops ;
inode->i_fop = &lfs_file_ops;
inode->i_private = &counter;
d_add ( dentry, inode) ;
printk ( KERN_INFO "Inode Created : %ld = %s", inode->i_ino, dentry->d_name.name) ;
return 0 ;
out:
printk ( KERN_INFO "Got BAD INODE.\n" ) ;
return -1 ;
}
struct inode *lfs_make_inode(struct super_block *sb, int mode)
{
struct inode *ret = new_inode(sb);
if (ret)
{
printk (KERN_INFO "Got good INODE.\n" ) ;
ret->i_mode = mode;
ret->i_uid = ret->i_gid = 0;
ret->i_blkbits = PAGE_CACHE_SIZE;
ret->i_blocks = 0;
ret->i_atime = ret->i_mtime = ret->i_ctime = CURRENT_TIME;
}
return ret;
}
On 3/12/07, Avishay Traeger <atraeger@xxxxxxxxxxxxx> wrote:
On Mon, 2007-03-12 at 20:10 +0530, Prasad Joshi wrote:
>
> Please someone help or at least point me to some more such links.
>
> Thanks and regards,
> Prasad.
Post all of your code and I (and hopefully others) will take a look.
Avishay
