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SubjectRe: SHM and programs unable to attach to shm segments
From
Date
Hi Linus,

The following patch adds the attach after remove feature to
2.3.99-pre2-3.

Greetings
Christoph

--
diff -uNr 99-pre2.3/Documentation/Changes c2-3/Documentation/Changes
--- 99-pre2.3/Documentation/Changes Fri Mar 17 09:40:08 2000
+++ c2-3/Documentation/Changes Fri Mar 17 20:06:28 2000
@@ -73,8 +73,7 @@
===================

To use System V shared memory, you have to mount the shm filesystem
-somewhere and put the mountpoint into /proc/sys/kernel/shmpath.
-Default is /var/shm.
+somewhere.

<CTRL><ALT><DEL> now performs a cold reboot instead of a warm reboot
for increased hardware compatibility. If you want a warm reboot and
diff -uNr 99-pre2.3/ipc/shm.c c2-3/ipc/shm.c
--- 99-pre2.3/ipc/shm.c Fri Mar 17 09:40:09 2000
+++ c2-3/ipc/shm.c Fri Mar 17 20:04:48 2000
@@ -20,6 +20,13 @@
* can only be mounted one time.
* 3) Read and write are not implemented (should they?)
* 4) No special nodes are supported
+ *
+ * There are the following mount options:
+ * - nr_blocks (^= shmall) is the number of blocks of size PAGE_SIZE
+ * we are allowed to allocate
+ * - nr_inodes (^= shmmni) is the number of files we are allowed to
+ * allocate
+ * - mode is the mode for the root directory (default S_IRWXUGO | S_ISVTX)
*/

#include <linux/config.h>
@@ -74,6 +81,7 @@
time_t ctime;
pid_t cpid;
pid_t lpid;
+ int unlinked;
int nlen;
char nm[0];
} shmem;
@@ -91,6 +99,7 @@
#define shm_lprid permap.shmem.lpid
#define shm_namelen permap.shmem.nlen
#define shm_name permap.shmem.nm
+#define shm_unlinked permap.shmem.unlinked
#define zsem permap.zero.sema
#define zero_list permap.zero.list

@@ -111,6 +120,7 @@
static void killseg_core(struct shmid_kernel *shp, int doacc);
static void shm_open (struct vm_area_struct *shmd);
static void shm_close (struct vm_area_struct *shmd);
+static void shm_remove_name(struct shmid_kernel *shp, int id);
static struct page * shm_nopage(struct vm_area_struct *, unsigned long, int);
static int shm_swapout(struct page *, struct file *);
#ifdef CONFIG_PROC_FS
@@ -435,7 +445,7 @@
continue;
if (!(shp = shm_get (nr-2)))
continue;
- if (shp->shm_perm.mode & SHM_DEST)
+ if (shp->shm_unlinked)
continue;
if (filldir(dirent, shp->shm_name, shp->shm_namelen, nr, nr) < 0 )
break;;
@@ -464,7 +474,7 @@
continue;
if (!(shp = shm_lock(i)))
continue;
- if (!(shp->shm_perm.mode & SHM_DEST) &&
+ if (!(shp->shm_unlinked) &&
dent->d_name.len == shp->shm_namelen &&
strncmp(dent->d_name.name, shp->shm_name, shp->shm_namelen) == 0)
goto found;
@@ -502,6 +512,7 @@
down (&shm_ids.sem);
if (!(shp = shm_lock (inode->i_ino)))
BUG();
+ shp->shm_unlinked = 1;
shp->shm_perm.mode |= SHM_DEST;
shp->shm_perm.key = IPC_PRIVATE; /* Do not find it any more */
shm_unlock (inode->i_ino);
@@ -633,16 +644,18 @@
static inline struct shmid_kernel *newseg_alloc(int numpages, size_t namelen)
{
struct shmid_kernel *shp;
+ pte_t **dir;

shp = (struct shmid_kernel *) kmalloc (sizeof (*shp) + namelen, GFP_KERNEL);
if (!shp)
- return 0;
+ return ERR_PTR(-ENOMEM);

- shp->shm_dir = shm_alloc (numpages);
- if (!shp->shm_dir) {
+ dir = shm_alloc (numpages);
+ if (IS_ERR(dir)) {
kfree(shp);
- return 0;
+ return ERR_PTR(PTR_ERR(dir));
}
+ shp->shm_dir = dir;
shp->shm_npages = numpages;
shp->shm_nattch = 0;
shp->shm_namelen = namelen;
@@ -664,8 +677,8 @@
if (shm_tot + numpages >= shm_ctlall)
return -ENOSPC;

- if (!(shp = newseg_alloc(numpages, namelen ? namelen : SHM_FMT_LEN + 1)))
- return -ENOMEM;
+ if (IS_ERR(shp = newseg_alloc(numpages, namelen ? namelen : SHM_FMT_LEN + 1)))
+ return PTR_ERR(shp);
id = ipc_addid(&shm_ids, &shp->shm_perm, shm_ctlmni+1);
if(id == -1) {
shm_free(shp->shm_dir,numpages);
@@ -680,6 +693,7 @@
shp->shm_atim = shp->shm_dtim = 0;
shp->shm_ctim = CURRENT_TIME;
shp->id = shm_buildid(id,shp->shm_perm.seq);
+ shp->shm_unlinked = 0;
if (namelen != 0) {
shp->shm_namelen = namelen;
memcpy (shp->shm_name, name, namelen);
@@ -1002,16 +1016,30 @@
}
case IPC_RMID:
{
- char name[SHM_FMT_LEN+1];
- if ((shmid % SEQ_MULTIPLIER)== zero_id)
- return -EINVAL;
- sprintf (name, SHM_FMT, shmid);
+ /*
+ * 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.
+ */
+
lock_kernel();
- err = do_unlink (name, dget(shm_sb->s_root));
+ if ((shmid % SEQ_MULTIPLIER) == zero_id)
+ return -EINVAL;
+ shp = shm_lock(shmid);
+ if(shp==NULL)
+ return -EINVAL;
+ if(shm_checkid(shp,shmid)!=0) {
+ shm_unlock(shmid);
+ return -EIDRM;
+ }
+
+ shp->shm_perm.mode |= SHM_DEST;
+ shp->shm_perm.key = IPC_PRIVATE; /* Do not find it any more */
+ shm_remove_name (shp, shmid);
unlock_kernel();
- if (err == -ENOENT)
- err = -EINVAL;
- return err;
+ return 0;
}

case IPC_SET:
@@ -1109,10 +1137,8 @@
sprintf (name, SHM_FMT, shmid);
lock_kernel();
file = filp_open(name, O_RDWR, 0, dget(shm_sb->s_root));
- if (IS_ERR (file)) {
- unlock_kernel();
+ if (IS_ERR (file))
goto bad_file;
- }
*raddr = do_mmap (file, addr, file->f_dentry->d_inode->i_size,
(shmflg & SHM_RDONLY ? PROT_READ :
PROT_READ | PROT_WRITE), flags, 0);
@@ -1125,6 +1151,7 @@
return err;

bad_file:
+ unlock_kernel();
if ((err = PTR_ERR(file)) == -ENOENT)
return -EINVAL;
return err;
@@ -1137,6 +1164,24 @@
}

/*
+ * Remove a name. Must be called with lock_kernel and the shmid
+ * locked. Will unlock the shmid.
+ */
+
+static void shm_remove_name(struct shmid_kernel *shp, int id)
+{
+ char name[SHM_FMT_LEN+1];
+
+ if(!(shp->shm_nattch == 0 && shp->shm_perm.mode & SHM_DEST)) {
+ shm_unlock(id);
+ return;
+ }
+ sprintf (name, SHM_FMT, id);
+ shm_unlock(id);
+ do_unlink (name, dget(shm_sb->s_root));
+}
+
+/*
* 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
@@ -1147,13 +1192,15 @@
int id = shmd->vm_file->f_dentry->d_inode->i_ino;
struct shmid_kernel *shp;

+ lock_kernel();
/* remove from the list of attaches of the shm segment */
if(!(shp = shm_lock(id)))
BUG();
shp->shm_lprid = current->pid;
shp->shm_dtim = CURRENT_TIME;
shp->shm_nattch--;
- shm_unlock(id);
+ shm_remove_name(shp, id);
+ unlock_kernel();
}

/*
@@ -1458,8 +1505,8 @@
continue;
shp = shm_lock(i);
if(shp!=NULL) {
-#define SMALL_STRING "%10d %10d %4o %10u %5u %5u %5d %5u %5u %5u %5u %10lu %10lu %10lu %.*s\n"
-#define BIG_STRING "%10d %10d %4o %21u %5u %5u %5d %5u %5u %5u %5u %10lu %10lu %10lu %.*s\n"
+#define SMALL_STRING "%10d %10d %4o %10u %5u %5u %5d %5u %5u %5u %5u %10lu %10lu %10lu %.*s%s\n"
+#define BIG_STRING "%10d %10d %4o %21u %5u %5u %5d %5u %5u %5u %5u %10lu %10lu %10lu %.*s%s\n"
char *format;

if (sizeof(size_t) <= sizeof(int))
@@ -1482,7 +1529,8 @@
shp->shm_dtim,
shp->shm_ctim,
shp->shm_namelen,
- shp->shm_name);
+ shp->shm_name,
+ shp->shm_unlinked ? " (deleted)" : "");
shm_unlock(i);

pos += len;
@@ -1571,8 +1619,8 @@

if (!vm_enough_memory((vma->vm_end - vma->vm_start) >> PAGE_SHIFT))
return -ENOMEM;
- if (!(shp = newseg_alloc((vma->vm_end - vma->vm_start) / PAGE_SIZE, 0)))
- return -ENOMEM;
+ if (IS_ERR(shp = newseg_alloc((vma->vm_end - vma->vm_start) / PAGE_SIZE, 0)))
+ return PTR_ERR(shp);
if ((filp = file_setup(vma->vm_file, shp)) == 0) {
killseg_core(shp, 0);
return -ENOMEM;
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