[PATCH] ipc: add generic struct ipc_ids seq_file iteration

The following two patches convert /proc/sysvipc/* to use seq_file.

This gives us the following:

- Self-consistent IPC records in proc.
- O(n) reading of the files themselves.

This patch:

Add a generic method for ipc types to be displayed using seq_file. This
patch abstracts out seq_file iterating over struct ipc_ids into ipc/util.c

Signed-off-by: Mike Waychison <[e-mail]>
Cc: Manfred Spraul <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

ipc/util.c

···
 #include <linux/security.h>
 #include <linux/rcupdate.h>
 #include <linux/workqueue.h>
+#include <linux/seq_file.h>
+#include <linux/proc_fs.h>
 
 #include <asm/unistd.h>
 
 #include "util.h"
+
+struct ipc_proc_iface {
+	const char *path;
+	const char *header;
+	struct ipc_ids *ids;
+	int (*show)(struct seq_file *, void *);
+};
 
 /**
  *	ipc_init	-	initialise IPC subsystem
···
 	for(i=0;i<size;i++)
 		ids->entries->p[i] = NULL;
 }
+
+#ifdef CONFIG_PROC_FS
+static struct file_operations sysvipc_proc_fops;
+/**
+ *	ipc_init_proc_interface	-  Create a proc interface for sysipc types
+ *				   using a seq_file interface.
+ *	@path: Path in procfs
+ *	@header: Banner to be printed at the beginning of the file.
+ *	@ids: ipc id table to iterate.
+ *	@show: show routine.
+ */
+void __init ipc_init_proc_interface(const char *path, const char *header,
+				    struct ipc_ids *ids,
+				    int (*show)(struct seq_file *, void *))
+{
+	struct proc_dir_entry *pde;
+	struct ipc_proc_iface *iface;
+
+	iface = kmalloc(sizeof(*iface), GFP_KERNEL);
+	if (!iface)
+		return;
+	iface->path	= path;
+	iface->header	= header;
+	iface->ids	= ids;
+	iface->show	= show;
+
+	pde = create_proc_entry(path,
+				S_IRUGO,        /* world readable */
+				NULL            /* parent dir */);
+	if (pde) {
+		pde->data = iface;
+		pde->proc_fops = &sysvipc_proc_fops;
+	} else {
+		kfree(iface);
+	}
+}
+#endif
 
 /**
  *	ipc_findkey	-	find a key in an ipc identifier set	
···
 }
 
 #endif /* __ARCH_WANT_IPC_PARSE_VERSION */
+
+#ifdef CONFIG_PROC_FS
+static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
+{
+	struct ipc_proc_iface *iface = s->private;
+	struct kern_ipc_perm *ipc = it;
+	loff_t p;
+
+	/* If we had an ipc id locked before, unlock it */
+	if (ipc && ipc != SEQ_START_TOKEN)
+		ipc_unlock(ipc);
+
+	/*
+	 * p = *pos - 1 (because id 0 starts at position 1)
+	 *          + 1 (because we increment the position by one)
+	 */
+	for (p = *pos; p <= iface->ids->max_id; p++) {
+		if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
+			*pos = p + 1;
+			return ipc;
+		}
+	}
+
+	/* Out of range - return NULL to terminate iteration */
+	return NULL;
+}
+
+/*
+ * File positions: pos 0 -> header, pos n -> ipc id + 1.
+ * SeqFile iterator: iterator value locked shp or SEQ_TOKEN_START.
+ */
+static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
+{
+	struct ipc_proc_iface *iface = s->private;
+	struct kern_ipc_perm *ipc;
+	loff_t p;
+
+	/*
+	 * Take the lock - this will be released by the corresponding
+	 * call to stop().
+	 */
+	down(&iface->ids->sem);
+
+	/* pos < 0 is invalid */
+	if (*pos < 0)
+		return NULL;
+
+	/* pos == 0 means header */
+	if (*pos == 0)
+		return SEQ_START_TOKEN;
+
+	/* Find the (pos-1)th ipc */
+	for (p = *pos - 1; p <= iface->ids->max_id; p++) {
+		if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
+			*pos = p + 1;
+			return ipc;
+		}
+	}
+	return NULL;
+}
+
+static void sysvipc_proc_stop(struct seq_file *s, void *it)
+{
+	struct kern_ipc_perm *ipc = it;
+	struct ipc_proc_iface *iface = s->private;
+
+	/* If we had a locked segment, release it */
+	if (ipc && ipc != SEQ_START_TOKEN)
+		ipc_unlock(ipc);
+
+	/* Release the lock we took in start() */
+	up(&iface->ids->sem);
+}
+
+static int sysvipc_proc_show(struct seq_file *s, void *it)
+{
+	struct ipc_proc_iface *iface = s->private;
+
+	if (it == SEQ_START_TOKEN)
+		return seq_puts(s, iface->header);
+
+	return iface->show(s, it);
+}
+
+static struct seq_operations sysvipc_proc_seqops = {
+	.start = sysvipc_proc_start,
+	.stop  = sysvipc_proc_stop,
+	.next  = sysvipc_proc_next,
+	.show  = sysvipc_proc_show,
+};
+
+static int sysvipc_proc_open(struct inode *inode, struct file *file) {
+	int ret;
+	struct seq_file *seq;
+
+	ret = seq_open(file, &sysvipc_proc_seqops);
+	if (!ret) {
+		seq = file->private_data;
+		seq->private = PDE(inode)->data;
+	}
+	return ret;
+}
+
+static struct file_operations sysvipc_proc_fops = {
+	.open    = sysvipc_proc_open,
+	.read    = seq_read,
+	.llseek  = seq_lseek,
+	.release = seq_release,
+};
+#endif /* CONFIG_PROC_FS */

ipc/util.h

···
 	struct ipc_id_ary* entries;
 };
 
+struct seq_file;
 void __init ipc_init_ids(struct ipc_ids* ids, int size);
+#ifdef CONFIG_PROC_FS
+void __init ipc_init_proc_interface(const char *path, const char *header,
+				    struct ipc_ids *ids,
+				    int (*show)(struct seq_file *, void *));
+#else
+#define ipc_init_proc_interface(path, header, ids, show) do {} while (0)
+#endif
 
 /* must be called with ids->sem acquired.*/
 int ipc_findkey(struct ipc_ids* ids, key_t key);