[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 <mikew@google.com>
Cc: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 164 insertions, 0 deletions

diff --git a/ipc/util.c b/ipc/util.c
index e00c35f7b2b8..10e836d0d89e 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -24,11 +24,20 @@
 #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
  *
@@ -86,6 +95,43 @@ void __init ipc_init_ids(struct ipc_ids* ids, int size)
                 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     
  *      @ids: Identifier set
@@ -578,3 +624,113 @@ int ipc_parse_version (int *cmd)
 }
 
 #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 */
diff --git a/ipc/util.h b/ipc/util.h
index 44348ca5a707..fc9a28be0797 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -30,7 +30,15 @@ struct ipc_ids {
         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);