um: resurrect the right variant of mconsole_proc()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/um/drivers/mconsole_kern.c

@@ -21,6 +21,9 @@
 #include <linux/un.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
+#include <linux/fs.h>
+#include <linux/mount.h>
+#include <linux/file.h>
 #include <asm/uaccess.h>
 #include <asm/switch_to.h>
 
@@ -118,18 +121,14 @@ void mconsole_log(struct mc_request *req)
 	mconsole_reply(req, "", 0, 0);
 }
 
-/* This is a more convoluted version of mconsole_proc, which has some stability
- * problems; however, we need it fixed, because it is expected that UML users
- * mount HPPFS instead of procfs on /proc. And we want mconsole_proc to still
- * show the real procfs content, not the ones from hppfs.*/
-#if 0
 void mconsole_proc(struct mc_request *req)
 {
 	struct vfsmount *mnt = current->nsproxy->pid_ns->proc_mnt;
+	char *buf;
+	int len;
 	struct file *file;
-	int n;
-	char *ptr = req->request.data, *buf;
-	mm_segment_t old_fs = get_fs();
+	int first_chunk = 1;
+	char *ptr = req->request.data;
 
 	ptr += strlen("proc");
 	ptr = skip_spaces(ptr);
@@ -137,6 +136,7 @@ void mconsole_proc(struct mc_request *req)
 	file = file_open_root(mnt->mnt_root, mnt, ptr, O_RDONLY);
 	if (IS_ERR(file)) {
 		mconsole_reply(req, "Failed to open file", 1, 0);
+		printk(KERN_ERR "open /proc/%s: %ld\n", ptr, PTR_ERR(file));
 		goto out;
 	}
 
@@ -146,62 +146,13 @@ void mconsole_proc(struct mc_request *req)
 		goto out_fput;
 	}
 
-	if (file->f_op->read) {
-		do {
-			loff_t pos;
-			set_fs(KERNEL_DS);
-			n = vfs_read(file, buf, PAGE_SIZE - 1, &pos);
-			file_pos_write(file, pos);
-			set_fs(old_fs);
-			if (n >= 0) {
-				buf[n] = '\0';
-				mconsole_reply(req, buf, 0, (n > 0));
-			}
-			else {
-				mconsole_reply(req, "Read of file failed",
-					       1, 0);
-				goto out_free;
-			}
-		} while (n > 0);
-	}
-	else mconsole_reply(req, "", 0, 0);
-
- out_free:
-	kfree(buf);
- out_fput:
-	fput(file);
- out: ;
-}
-#endif
-
-void mconsole_proc(struct mc_request *req)
-{
-	char path[64];
-	char *buf;
-	int len;
-	int fd;
-	int first_chunk = 1;
-	char *ptr = req->request.data;
-
-	ptr += strlen("proc");
-	ptr = skip_spaces(ptr);
-	snprintf(path, sizeof(path), "/proc/%s", ptr);
-
-	fd = sys_open(path, 0, 0);
-	if (fd < 0) {
-		mconsole_reply(req, "Failed to open file", 1, 0);
-		printk(KERN_ERR "open %s: %d\n",path,fd);
-		goto out;
-	}
-
-	buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
-	if (buf == NULL) {
-		mconsole_reply(req, "Failed to allocate buffer", 1, 0);
-		goto out_close;
-	}
-
-	for (;;) {
-		len = sys_read(fd, buf, PAGE_SIZE-1);
+	do {
+		loff_t pos;
+		mm_segment_t old_fs = get_fs();
+		set_fs(KERNEL_DS);
+		len = vfs_read(file, buf, PAGE_SIZE - 1, &pos);
+		set_fs(old_fs);
+		file->f_pos = pos;
 		if (len < 0) {
 			mconsole_reply(req, "Read of file failed", 1, 0);
 			goto out_free;
@@ -211,22 +162,14 @@ void mconsole_proc(struct mc_request *req)
 			mconsole_reply(req, "\n", 0, 1);
 			first_chunk = 0;
 		}
-		if (len == PAGE_SIZE-1) {
-			buf[len] = '\0';
-			mconsole_reply(req, buf, 0, 1);
-		} else {
-			buf[len] = '\0';
-			mconsole_reply(req, buf, 0, 0);
-			break;
-		}
-	}
-
+		buf[len] = '\0';
+		mconsole_reply(req, buf, 0, (len > 0));
+	} while (len > 0);
  out_free:
 	kfree(buf);
- out_close:
-	sys_close(fd);
- out:
-	/* nothing */;
+ out_fput:
+	fput(file);
+ out: ;
 }
 
 #define UML_MCONSOLE_HELPTEXT \