[Bluetooth] Fix uninitialized return value for RFCOMM sendmsg()

[linux/fpc-iii.git] / ipc / shm.c

/*
 * linux/ipc/shm.c
 * Copyright (C) 1992, 1993 Krishna Balasubramanian
 *       Many improvements/fixes by Bruno Haible.
 * Replaced `struct shm_desc' by `struct vm_area_struct', July 1994.
 * Fixed the shm swap deallocation (shm_unuse()), August 1998 Andrea Arcangeli.
 *
 * /proc/sysvipc/shm support (c) 1999 Dragos Acostachioaie <dragos@iname.com>
 * BIGMEM support, Andrea Arcangeli <andrea@suse.de>
 * SMP thread shm, Jean-Luc Boyard <jean-luc.boyard@siemens.fr>
 * HIGHMEM support, Ingo Molnar <mingo@redhat.com>
 * Make shmmax, shmall, shmmni sysctl'able, Christoph Rohland <cr@sap.com>
 * Shared /dev/zero support, Kanoj Sarcar <kanoj@sgi.com>
 * Move the mm functionality over to mm/shmem.c, Christoph Rohland <cr@sap.com>
 *
 */

#include <linux/config.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/init.h>
#include <linux/file.h>
#include <linux/mman.h>
#include <linux/shmem_fs.h>
#include <linux/security.h>
#include <linux/syscalls.h>
#include <linux/audit.h>
#include <linux/capability.h>
#include <linux/ptrace.h>
#include <linux/seq_file.h>

#include <asm/uaccess.h>

#include "util.h"

static struct file_operations shm_file_operations;
static struct vm_operations_struct shm_vm_ops;

static struct ipc_ids shm_ids;

#define shm_lock(id)    ((struct shmid_kernel*)ipc_lock(&shm_ids,id))
#define shm_unlock(shp) ipc_unlock(&(shp)->shm_perm)
#define shm_get(id)     ((struct shmid_kernel*)ipc_get(&shm_ids,id))
#define shm_buildid(id, seq) \
        ipc_buildid(&shm_ids, id, seq)

static int newseg (key_t key, int shmflg, size_t size);
static void shm_open (struct vm_area_struct *shmd);
static void shm_close (struct vm_area_struct *shmd);
#ifdef CONFIG_PROC_FS
static int sysvipc_shm_proc_show(struct seq_file *s, void *it);
#endif

size_t  shm_ctlmax = SHMMAX;
size_t  shm_ctlall = SHMALL;
int     shm_ctlmni = SHMMNI;

static int shm_tot; /* total number of shared memory pages */

void __init shm_init (void)
{
        ipc_init_ids(&shm_ids, 1);
        ipc_init_proc_interface("sysvipc/shm",
                                "       key      shmid perms       size  cpid  lpid nattch   uid   gid  cuid  cgid      atime      dtime      ctime\n",
                                &shm_ids,
                                sysvipc_shm_proc_show);
}

static inline int shm_checkid(struct shmid_kernel *s, int id)
{
        if (ipc_checkid(&shm_ids,&s->shm_perm,id))
                return -EIDRM;
        return 0;
}

static inline struct shmid_kernel *shm_rmid(int id)
{
        return (struct shmid_kernel *)ipc_rmid(&shm_ids,id);
}

static inline int shm_addid(struct shmid_kernel *shp)
{
        return ipc_addid(&shm_ids, &shp->shm_perm, shm_ctlmni);
}



static inline void shm_inc (int id) {
        struct shmid_kernel *shp;

        if(!(shp = shm_lock(id)))
                BUG();
        shp->shm_atim = get_seconds();
        shp->shm_lprid = current->tgid;
        shp->shm_nattch++;
        shm_unlock(shp);
}

/* This is called by fork, once for every shm attach. */
static void shm_open (struct vm_area_struct *shmd)
{
        shm_inc (shmd->vm_file->f_dentry->d_inode->i_ino);
}

/*
 * shm_destroy - free the struct shmid_kernel
 *
 * @shp: struct to free
 *
 * It has to be called with shp and shm_ids.sem locked,
 * but returns with shp unlocked and freed.
 */
static void shm_destroy (struct shmid_kernel *shp)
{
        shm_tot -= (shp->shm_segsz + PAGE_SIZE - 1) >> PAGE_SHIFT;
        shm_rmid (shp->id);
        shm_unlock(shp);
        if (!is_file_hugepages(shp->shm_file))
                shmem_lock(shp->shm_file, 0, shp->mlock_user);
        else
                user_shm_unlock(shp->shm_file->f_dentry->d_inode->i_size,
                                                shp->mlock_user);
        fput (shp->shm_file);
        security_shm_free(shp);
        ipc_rcu_putref(shp);
}

/*
 * remove the attach descriptor shmd.
 * free memory for segment if it is marked destroyed.
 * The descriptor has already been removed from the current->mm->mmap list
 * and will later be kfree()d.
 */
static void shm_close (struct vm_area_struct *shmd)
{
        struct file * file = shmd->vm_file;
        int id = file->f_dentry->d_inode->i_ino;
        struct shmid_kernel *shp;

        down (&shm_ids.sem);
        /* remove from the list of attaches of the shm segment */
        if(!(shp = shm_lock(id)))
                BUG();
        shp->shm_lprid = current->tgid;
        shp->shm_dtim = get_seconds();
        shp->shm_nattch--;
        if(shp->shm_nattch == 0 &&
           shp->shm_perm.mode & SHM_DEST)
                shm_destroy (shp);
        else
                shm_unlock(shp);
        up (&shm_ids.sem);
}

static int shm_mmap(struct file * file, struct vm_area_struct * vma)
{
        int ret;

        ret = shmem_mmap(file, vma);
        if (ret == 0) {
                vma->vm_ops = &shm_vm_ops;
                if (!(vma->vm_flags & VM_WRITE))
                        vma->vm_flags &= ~VM_MAYWRITE;
                shm_inc(file->f_dentry->d_inode->i_ino);
        }

        return ret;
}

static struct file_operations shm_file_operations = {
        .mmap   = shm_mmap,
#ifndef CONFIG_MMU
        .get_unmapped_area = shmem_get_unmapped_area,
#endif
};

static struct vm_operations_struct shm_vm_ops = {
        .open   = shm_open,     /* callback for a new vm-area open */
        .close  = shm_close,    /* callback for when the vm-area is released */
        .nopage = shmem_nopage,
#if defined(CONFIG_NUMA) && defined(CONFIG_SHMEM)
        .set_policy = shmem_set_policy,
        .get_policy = shmem_get_policy,
#endif
};

static int newseg (key_t key, int shmflg, size_t size)
{
        int error;
        struct shmid_kernel *shp;
        int numpages = (size + PAGE_SIZE -1) >> PAGE_SHIFT;
        struct file * file;
        char name[13];
        int id;

        if (size < SHMMIN || size > shm_ctlmax)
                return -EINVAL;

        if (shm_tot + numpages >= shm_ctlall)
                return -ENOSPC;

        shp = ipc_rcu_alloc(sizeof(*shp));
        if (!shp)
                return -ENOMEM;

        shp->shm_perm.key = key;
        shp->shm_perm.mode = (shmflg & S_IRWXUGO);
        shp->mlock_user = NULL;

        shp->shm_perm.security = NULL;
        error = security_shm_alloc(shp);
        if (error) {
                ipc_rcu_putref(shp);
                return error;
        }

        if (shmflg & SHM_HUGETLB) {
                /* hugetlb_zero_setup takes care of mlock user accounting */
                file = hugetlb_zero_setup(size);
                shp->mlock_user = current->user;
        } else {
                int acctflag = VM_ACCOUNT;
                /*
                 * Do not allow no accounting for OVERCOMMIT_NEVER, even
                 * if it's asked for.
                 */
                if  ((shmflg & SHM_NORESERVE) &&
                                sysctl_overcommit_memory != OVERCOMMIT_NEVER)
                        acctflag = 0;
                sprintf (name, "SYSV%08x", key);
                file = shmem_file_setup(name, size, acctflag);
        }
        error = PTR_ERR(file);
        if (IS_ERR(file))
                goto no_file;

        error = -ENOSPC;
        id = shm_addid(shp);
        if(id == -1) 
                goto no_id;

        shp->shm_cprid = current->tgid;
        shp->shm_lprid = 0;
        shp->shm_atim = shp->shm_dtim = 0;
        shp->shm_ctim = get_seconds();
        shp->shm_segsz = size;
        shp->shm_nattch = 0;
        shp->id = shm_buildid(id,shp->shm_perm.seq);
        shp->shm_file = file;
        file->f_dentry->d_inode->i_ino = shp->id;

        /* Hugetlb ops would have already been assigned. */
        if (!(shmflg & SHM_HUGETLB))
                file->f_op = &shm_file_operations;

        shm_tot += numpages;
        shm_unlock(shp);
        return shp->id;

no_id:
        fput(file);
no_file:
        security_shm_free(shp);
        ipc_rcu_putref(shp);
        return error;
}

asmlinkage long sys_shmget (key_t key, size_t size, int shmflg)
{
        struct shmid_kernel *shp;
        int err, id = 0;

        down(&shm_ids.sem);
        if (key == IPC_PRIVATE) {
                err = newseg(key, shmflg, size);
        } else if ((id = ipc_findkey(&shm_ids, key)) == -1) {
                if (!(shmflg & IPC_CREAT))
                        err = -ENOENT;
                else
                        err = newseg(key, shmflg, size);
        } else if ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) {
                err = -EEXIST;
        } else {
                shp = shm_lock(id);
                if(shp==NULL)
                        BUG();
                if (shp->shm_segsz < size)
                        err = -EINVAL;
                else if (ipcperms(&shp->shm_perm, shmflg))
                        err = -EACCES;
                else {
                        int shmid = shm_buildid(id, shp->shm_perm.seq);
                        err = security_shm_associate(shp, shmflg);
                        if (!err)
                                err = shmid;
                }
                shm_unlock(shp);
        }
        up(&shm_ids.sem);

        return err;
}

static inline unsigned long copy_shmid_to_user(void __user *buf, struct shmid64_ds *in, int version)
{
        switch(version) {
        case IPC_64:
                return copy_to_user(buf, in, sizeof(*in));
        case IPC_OLD:
            {
                struct shmid_ds out;

                ipc64_perm_to_ipc_perm(&in->shm_perm, &out.shm_perm);
                out.shm_segsz   = in->shm_segsz;
                out.shm_atime   = in->shm_atime;
                out.shm_dtime   = in->shm_dtime;
                out.shm_ctime   = in->shm_ctime;
                out.shm_cpid    = in->shm_cpid;
                out.shm_lpid    = in->shm_lpid;
                out.shm_nattch  = in->shm_nattch;

                return copy_to_user(buf, &out, sizeof(out));
            }
        default:
                return -EINVAL;
        }
}

struct shm_setbuf {
        uid_t   uid;
        gid_t   gid;
        mode_t  mode;
};      

static inline unsigned long copy_shmid_from_user(struct shm_setbuf *out, void __user *buf, int version)
{
        switch(version) {
        case IPC_64:
            {
                struct shmid64_ds tbuf;

                if (copy_from_user(&tbuf, buf, sizeof(tbuf)))
                        return -EFAULT;

                out->uid        = tbuf.shm_perm.uid;
                out->gid        = tbuf.shm_perm.gid;
                out->mode       = tbuf.shm_perm.mode;

                return 0;
            }
        case IPC_OLD:
            {
                struct shmid_ds tbuf_old;

                if (copy_from_user(&tbuf_old, buf, sizeof(tbuf_old)))
                        return -EFAULT;

                out->uid        = tbuf_old.shm_perm.uid;
                out->gid        = tbuf_old.shm_perm.gid;
                out->mode       = tbuf_old.shm_perm.mode;

                return 0;
            }
        default:
                return -EINVAL;
        }
}

static inline unsigned long copy_shminfo_to_user(void __user *buf, struct shminfo64 *in, int version)
{
        switch(version) {
        case IPC_64:
                return copy_to_user(buf, in, sizeof(*in));
        case IPC_OLD:
            {
                struct shminfo out;

                if(in->shmmax > INT_MAX)
                        out.shmmax = INT_MAX;
                else
                        out.shmmax = (int)in->shmmax;

                out.shmmin      = in->shmmin;
                out.shmmni      = in->shmmni;
                out.shmseg      = in->shmseg;
                out.shmall      = in->shmall; 

                return copy_to_user(buf, &out, sizeof(out));
            }
        default:
                return -EINVAL;
        }
}

static void shm_get_stat(unsigned long *rss, unsigned long *swp) 
{
        int i;

        *rss = 0;
        *swp = 0;

        for (i = 0; i <= shm_ids.max_id; i++) {
                struct shmid_kernel *shp;
                struct inode *inode;

                shp = shm_get(i);
                if(!shp)
                        continue;

                inode = shp->shm_file->f_dentry->d_inode;

                if (is_file_hugepages(shp->shm_file)) {
                        struct address_space *mapping = inode->i_mapping;
                        *rss += (HPAGE_SIZE/PAGE_SIZE)*mapping->nrpages;
                } else {
                        struct shmem_inode_info *info = SHMEM_I(inode);
                        spin_lock(&info->lock);
                        *rss += inode->i_mapping->nrpages;
                        *swp += info->swapped;
                        spin_unlock(&info->lock);
                }
        }
}

asmlinkage long sys_shmctl (int shmid, int cmd, struct shmid_ds __user *buf)
{
        struct shm_setbuf setbuf;
        struct shmid_kernel *shp;
        int err, version;

        if (cmd < 0 || shmid < 0) {
                err = -EINVAL;
                goto out;
        }

        version = ipc_parse_version(&cmd);

        switch (cmd) { /* replace with proc interface ? */
        case IPC_INFO:
        {
                struct shminfo64 shminfo;

                err = security_shm_shmctl(NULL, cmd);
                if (err)
                        return err;

                memset(&shminfo,0,sizeof(shminfo));
                shminfo.shmmni = shminfo.shmseg = shm_ctlmni;
                shminfo.shmmax = shm_ctlmax;
                shminfo.shmall = shm_ctlall;

                shminfo.shmmin = SHMMIN;
                if(copy_shminfo_to_user (buf, &shminfo, version))
                        return -EFAULT;
                /* reading a integer is always atomic */
                err= shm_ids.max_id;
                if(err<0)
                        err = 0;
                goto out;
        }
        case SHM_INFO:
        {
                struct shm_info shm_info;

                err = security_shm_shmctl(NULL, cmd);
                if (err)
                        return err;

                memset(&shm_info,0,sizeof(shm_info));
                down(&shm_ids.sem);
                shm_info.used_ids = shm_ids.in_use;
                shm_get_stat (&shm_info.shm_rss, &shm_info.shm_swp);
                shm_info.shm_tot = shm_tot;
                shm_info.swap_attempts = 0;
                shm_info.swap_successes = 0;
                err = shm_ids.max_id;
                up(&shm_ids.sem);
                if(copy_to_user (buf, &shm_info, sizeof(shm_info))) {
                        err = -EFAULT;
                        goto out;
                }

                err = err < 0 ? 0 : err;
                goto out;
        }
        case SHM_STAT:
        case IPC_STAT:
        {
                struct shmid64_ds tbuf;
                int result;
                memset(&tbuf, 0, sizeof(tbuf));
                shp = shm_lock(shmid);
                if(shp==NULL) {
                        err = -EINVAL;
                        goto out;
                } else if(cmd==SHM_STAT) {
                        err = -EINVAL;
                        if (shmid > shm_ids.max_id)
                                goto out_unlock;
                        result = shm_buildid(shmid, shp->shm_perm.seq);
                } else {
                        err = shm_checkid(shp,shmid);
                        if(err)
                                goto out_unlock;
                        result = 0;
                }
                err=-EACCES;
                if (ipcperms (&shp->shm_perm, S_IRUGO))
                        goto out_unlock;
                err = security_shm_shmctl(shp, cmd);
                if (err)
                        goto out_unlock;
                kernel_to_ipc64_perm(&shp->shm_perm, &tbuf.shm_perm);
                tbuf.shm_segsz  = shp->shm_segsz;
                tbuf.shm_atime  = shp->shm_atim;
                tbuf.shm_dtime  = shp->shm_dtim;
                tbuf.shm_ctime  = shp->shm_ctim;
                tbuf.shm_cpid   = shp->shm_cprid;
                tbuf.shm_lpid   = shp->shm_lprid;
                if (!is_file_hugepages(shp->shm_file))
                        tbuf.shm_nattch = shp->shm_nattch;
                else
                        tbuf.shm_nattch = file_count(shp->shm_file) - 1;
                shm_unlock(shp);
                if(copy_shmid_to_user (buf, &tbuf, version))
                        err = -EFAULT;
                else
                        err = result;
                goto out;
        }
        case SHM_LOCK:
        case SHM_UNLOCK:
        {
                shp = shm_lock(shmid);
                if(shp==NULL) {
                        err = -EINVAL;
                        goto out;
                }
                err = shm_checkid(shp,shmid);
                if(err)
                        goto out_unlock;

                if (!capable(CAP_IPC_LOCK)) {
                        err = -EPERM;
                        if (current->euid != shp->shm_perm.uid &&
                            current->euid != shp->shm_perm.cuid)
                                goto out_unlock;
                        if (cmd == SHM_LOCK &&
                            !current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur)
                                goto out_unlock;
                }

                err = security_shm_shmctl(shp, cmd);
                if (err)
                        goto out_unlock;
                
                if(cmd==SHM_LOCK) {
                        struct user_struct * user = current->user;
                        if (!is_file_hugepages(shp->shm_file)) {
                                err = shmem_lock(shp->shm_file, 1, user);
                                if (!err) {
                                        shp->shm_perm.mode |= SHM_LOCKED;
                                        shp->mlock_user = user;
                                }
                        }
                } else if (!is_file_hugepages(shp->shm_file)) {
                        shmem_lock(shp->shm_file, 0, shp->mlock_user);
                        shp->shm_perm.mode &= ~SHM_LOCKED;
                        shp->mlock_user = NULL;
                }
                shm_unlock(shp);
                goto out;
        }
        case IPC_RMID:
        {
                /*
                 *      We cannot simply remove the file. The SVID states
                 *      that the block remains until the last person
                 *      detaches from it, then is deleted. A shmat() on
                 *      an RMID segment is legal in older Linux and if 
                 *      we change it apps break...
                 *
                 *      Instead we set a destroyed flag, and then blow
                 *      the name away when the usage hits zero.
                 */
                down(&shm_ids.sem);
                shp = shm_lock(shmid);
                err = -EINVAL;
                if (shp == NULL) 
                        goto out_up;
                err = shm_checkid(shp, shmid);
                if(err)
                        goto out_unlock_up;

                if (current->euid != shp->shm_perm.uid &&
                    current->euid != shp->shm_perm.cuid && 
                    !capable(CAP_SYS_ADMIN)) {
                        err=-EPERM;
                        goto out_unlock_up;
                }

                err = security_shm_shmctl(shp, cmd);
                if (err)
                        goto out_unlock_up;

                if (shp->shm_nattch){
                        shp->shm_perm.mode |= SHM_DEST;
                        /* Do not find it any more */
                        shp->shm_perm.key = IPC_PRIVATE;
                        shm_unlock(shp);
                } else
                        shm_destroy (shp);
                up(&shm_ids.sem);
                goto out;
        }

        case IPC_SET:
        {
                if (copy_shmid_from_user (&setbuf, buf, version)) {
                        err = -EFAULT;
                        goto out;
                }
                if ((err = audit_ipc_perms(0, setbuf.uid, setbuf.gid, setbuf.mode)))
                        return err;
                down(&shm_ids.sem);
                shp = shm_lock(shmid);
                err=-EINVAL;
                if(shp==NULL)
                        goto out_up;
                err = shm_checkid(shp,shmid);
                if(err)
                        goto out_unlock_up;
                err=-EPERM;
                if (current->euid != shp->shm_perm.uid &&
                    current->euid != shp->shm_perm.cuid && 
                    !capable(CAP_SYS_ADMIN)) {
                        goto out_unlock_up;
                }

                err = security_shm_shmctl(shp, cmd);
                if (err)
                        goto out_unlock_up;
                
                shp->shm_perm.uid = setbuf.uid;
                shp->shm_perm.gid = setbuf.gid;
                shp->shm_perm.mode = (shp->shm_perm.mode & ~S_IRWXUGO)
                        | (setbuf.mode & S_IRWXUGO);
                shp->shm_ctim = get_seconds();
                break;
        }

        default:
                err = -EINVAL;
                goto out;
        }

        err = 0;
out_unlock_up:
        shm_unlock(shp);
out_up:
        up(&shm_ids.sem);
        goto out;
out_unlock:
        shm_unlock(shp);
out:
        return err;
}

/*
 * Fix shmaddr, allocate descriptor, map shm, add attach descriptor to lists.
 *
 * NOTE! Despite the name, this is NOT a direct system call entrypoint. The
 * "raddr" thing points to kernel space, and there has to be a wrapper around
 * this.
 */
long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr)
{
        struct shmid_kernel *shp;
        unsigned long addr;
        unsigned long size;
        struct file * file;
        int    err;
        unsigned long flags;
        unsigned long prot;
        unsigned long o_flags;
        int acc_mode;
        void *user_addr;

        if (shmid < 0) {
                err = -EINVAL;
                goto out;
        } else if ((addr = (ulong)shmaddr)) {
                if (addr & (SHMLBA-1)) {
                        if (shmflg & SHM_RND)
                                addr &= ~(SHMLBA-1);       /* round down */
                        else
#ifndef __ARCH_FORCE_SHMLBA
                                if (addr & ~PAGE_MASK)
#endif
                                        return -EINVAL;
                }
                flags = MAP_SHARED | MAP_FIXED;
        } else {
                if ((shmflg & SHM_REMAP))
                        return -EINVAL;

                flags = MAP_SHARED;
        }

        if (shmflg & SHM_RDONLY) {
                prot = PROT_READ;
                o_flags = O_RDONLY;
                acc_mode = S_IRUGO;
        } else {
                prot = PROT_READ | PROT_WRITE;
                o_flags = O_RDWR;
                acc_mode = S_IRUGO | S_IWUGO;
        }
        if (shmflg & SHM_EXEC) {
                prot |= PROT_EXEC;
                acc_mode |= S_IXUGO;
        }

        /*
         * We cannot rely on the fs check since SYSV IPC does have an
         * additional creator id...
         */
        shp = shm_lock(shmid);
        if(shp == NULL) {
                err = -EINVAL;
                goto out;
        }
        err = shm_checkid(shp,shmid);
        if (err) {
                shm_unlock(shp);
                goto out;
        }
        if (ipcperms(&shp->shm_perm, acc_mode)) {
                shm_unlock(shp);
                err = -EACCES;
                goto out;
        }

        err = security_shm_shmat(shp, shmaddr, shmflg);
        if (err) {
                shm_unlock(shp);
                return err;
        }
                
        file = shp->shm_file;
        size = i_size_read(file->f_dentry->d_inode);
        shp->shm_nattch++;
        shm_unlock(shp);

        down_write(&current->mm->mmap_sem);
        if (addr && !(shmflg & SHM_REMAP)) {
                user_addr = ERR_PTR(-EINVAL);
                if (find_vma_intersection(current->mm, addr, addr + size))
                        goto invalid;
                /*
                 * If shm segment goes below stack, make sure there is some
                 * space left for the stack to grow (at least 4 pages).
                 */
                if (addr < current->mm->start_stack &&
                    addr > current->mm->start_stack - size - PAGE_SIZE * 5)
                        goto invalid;
        }
                
        user_addr = (void*) do_mmap (file, addr, size, prot, flags, 0);

invalid:
        up_write(&current->mm->mmap_sem);

        down (&shm_ids.sem);
        if(!(shp = shm_lock(shmid)))
                BUG();
        shp->shm_nattch--;
        if(shp->shm_nattch == 0 &&
           shp->shm_perm.mode & SHM_DEST)
                shm_destroy (shp);
        else
                shm_unlock(shp);
        up (&shm_ids.sem);

        *raddr = (unsigned long) user_addr;
        err = 0;
        if (IS_ERR(user_addr))
                err = PTR_ERR(user_addr);
out:
        return err;
}

asmlinkage long sys_shmat(int shmid, char __user *shmaddr, int shmflg)
{
        unsigned long ret;
        long err;

        err = do_shmat(shmid, shmaddr, shmflg, &ret);
        if (err)
                return err;
        force_successful_syscall_return();
        return (long)ret;
}

/*
 * detach and kill segment if marked destroyed.
 * The work is done in shm_close.
 */
asmlinkage long sys_shmdt(char __user *shmaddr)
{
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma, *next;
        unsigned long addr = (unsigned long)shmaddr;
        loff_t size = 0;
        int retval = -EINVAL;

        down_write(&mm->mmap_sem);

        /*
         * This function tries to be smart and unmap shm segments that
         * were modified by partial mlock or munmap calls:
         * - It first determines the size of the shm segment that should be
         *   unmapped: It searches for a vma that is backed by shm and that
         *   started at address shmaddr. It records it's size and then unmaps
         *   it.
         * - Then it unmaps all shm vmas that started at shmaddr and that
         *   are within the initially determined size.
         * Errors from do_munmap are ignored: the function only fails if
         * it's called with invalid parameters or if it's called to unmap
         * a part of a vma. Both calls in this function are for full vmas,
         * the parameters are directly copied from the vma itself and always
         * valid - therefore do_munmap cannot fail. (famous last words?)
         */
        /*
         * If it had been mremap()'d, the starting address would not
         * match the usual checks anyway. So assume all vma's are
         * above the starting address given.
         */
        vma = find_vma(mm, addr);

        while (vma) {
                next = vma->vm_next;

                /*
                 * Check if the starting address would match, i.e. it's
                 * a fragment created by mprotect() and/or munmap(), or it
                 * otherwise it starts at this address with no hassles.
                 */
                if ((vma->vm_ops == &shm_vm_ops || is_vm_hugetlb_page(vma)) &&
                        (vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) {


                        size = vma->vm_file->f_dentry->d_inode->i_size;
                        do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
                        /*
                         * We discovered the size of the shm segment, so
                         * break out of here and fall through to the next
                         * loop that uses the size information to stop
                         * searching for matching vma's.
                         */
                        retval = 0;
                        vma = next;
                        break;
                }
                vma = next;
        }

        /*
         * We need look no further than the maximum address a fragment
         * could possibly have landed at. Also cast things to loff_t to
         * prevent overflows and make comparisions vs. equal-width types.
         */
        size = PAGE_ALIGN(size);
        while (vma && (loff_t)(vma->vm_end - addr) <= size) {
                next = vma->vm_next;

                /* finding a matching vma now does not alter retval */
                if ((vma->vm_ops == &shm_vm_ops || is_vm_hugetlb_page(vma)) &&
                        (vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff)

                        do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
                vma = next;
        }

        up_write(&mm->mmap_sem);
        return retval;
}

#ifdef CONFIG_PROC_FS
static int sysvipc_shm_proc_show(struct seq_file *s, void *it)
{
        struct shmid_kernel *shp = it;
        char *format;

#define SMALL_STRING "%10d %10d  %4o %10u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"
#define BIG_STRING   "%10d %10d  %4o %21u %5u %5u  %5d %5u %5u %5u %5u %10lu %10lu %10lu\n"

        if (sizeof(size_t) <= sizeof(int))
                format = SMALL_STRING;
        else
                format = BIG_STRING;
        return seq_printf(s, format,
                          shp->shm_perm.key,
                          shp->id,
                          shp->shm_perm.mode,
                          shp->shm_segsz,
                          shp->shm_cprid,
                          shp->shm_lprid,
                          is_file_hugepages(shp->shm_file) ? (file_count(shp->shm_file) - 1) : shp->shm_nattch,
                          shp->shm_perm.uid,
                          shp->shm_perm.gid,
                          shp->shm_perm.cuid,
                          shp->shm_perm.cgid,
                          shp->shm_atim,
                          shp->shm_dtim,
                          shp->shm_ctim);
}
#endif