aufs: ioctl, brinfo

Provide info about the branches, which will be used from user-space.
This is essentially equivalent to the entries under sysfs
(/sys/fs/aufs/si_*/).
But the ioctl behaviour is atomic and never confuse the matching of the
branch id.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/ioctl.c

@@ -115,6 +115,10 @@ long aufs_ioctl_dir(struct file *file, unsigned int cmd, unsigned long arg)
 		err = au_wbr_fd(&file->f_path, (void __user *)arg);
 		break;
 
+	case AUFS_CTL_BRINFO:
+		err = au_brinfo_ioctl(file, arg);
+		break;
+
 	default:
 		/* do not call the lower */
 		AuDbg("0x%x\n", cmd);
@@ -150,7 +154,14 @@ long aufs_compat_ioctl_dir(struct file *file, unsigned int cmd,
 {
 	long err;
 
-	err = aufs_ioctl_dir(file, cmd, arg);
+	switch (cmd) {
+	case AUFS_CTL_BRINFO:
+		err = au_brinfo_compat_ioctl(file, arg);
+		break;
+
+	default:
+		err = aufs_ioctl_dir(file, cmd, arg);
+	}
 
 	AuTraceErr(err);
 	return err;

fs/aufs/sysaufs.h

@@ -57,6 +57,10 @@ extern struct attribute_group *sysaufs_attr_group;
 int sysaufs_si_xi_path(struct seq_file *seq, struct super_block *sb);
 ssize_t sysaufs_si_show(struct kobject *kobj, struct attribute *attr,
 			 char *buf);
+long au_brinfo_ioctl(struct file *file, unsigned long arg);
+#ifdef CONFIG_COMPAT
+long au_brinfo_compat_ioctl(struct file *file, unsigned long arg);
+#endif
 
 void sysaufs_br_init(struct au_branch *br);
 void sysaufs_brs_add(struct super_block *sb, aufs_bindex_t bindex);

fs/aufs/sysfs.c

@@ -7,6 +7,7 @@
  * sysfs interface
  */
 
+#include <linux/compat.h>
 #include <linux/seq_file.h>
 #include "aufs.h"
 
@@ -182,6 +183,91 @@ out:
 
 /* ---------------------------------------------------------------------- */
 
+static int au_brinfo(struct super_block *sb, union aufs_brinfo __user *arg)
+{
+	int err;
+	int16_t brid;
+	aufs_bindex_t bindex, bbot;
+	size_t sz;
+	char *buf;
+	struct seq_file *seq;
+	struct au_branch *br;
+
+	si_read_lock(sb, AuLock_FLUSH);
+	bbot = au_sbbot(sb);
+	err = bbot + 1;
+	if (!arg)
+		goto out;
+
+	err = -ENOMEM;
+	buf = (void *)__get_free_page(GFP_NOFS);
+	if (unlikely(!buf))
+		goto out;
+
+	seq = au_seq(buf, PAGE_SIZE);
+	err = PTR_ERR(seq);
+	if (IS_ERR(seq))
+		goto out_buf;
+
+	sz = sizeof(*arg) - offsetof(union aufs_brinfo, path);
+	for (bindex = 0; bindex <= bbot; bindex++, arg++) {
+		/* VERIFY_WRITE */
+		err = !access_ok(arg, sizeof(*arg));
+		if (unlikely(err))
+			break;
+
+		br = au_sbr(sb, bindex);
+		brid = br->br_id;
+		BUILD_BUG_ON(sizeof(brid) != sizeof(arg->id));
+		err = __put_user(brid, &arg->id);
+		if (unlikely(err))
+			break;
+
+		BUILD_BUG_ON(sizeof(br->br_perm) != sizeof(arg->perm));
+		err = __put_user(br->br_perm, &arg->perm);
+		if (unlikely(err))
+			break;
+
+		err = au_seq_path(seq, &br->br_path);
+		if (unlikely(err))
+			break;
+		seq_putc(seq, '\0');
+		if (!seq_has_overflowed(seq)) {
+			err = copy_to_user(arg->path, seq->buf, seq->count);
+			seq->count = 0;
+			if (unlikely(err))
+				break;
+		} else {
+			err = -E2BIG;
+			goto out_seq;
+		}
+	}
+	if (unlikely(err))
+		err = -EFAULT;
+
+out_seq:
+	au_kfree_rcu(seq);
+out_buf:
+	free_page((unsigned long)buf);
+out:
+	si_read_unlock(sb);
+	return err;
+}
+
+long au_brinfo_ioctl(struct file *file, unsigned long arg)
+{
+	return au_brinfo(file->f_path.dentry->d_sb, (void __user *)arg);
+}
+
+#ifdef CONFIG_COMPAT
+long au_brinfo_compat_ioctl(struct file *file, unsigned long arg)
+{
+	return au_brinfo(file->f_path.dentry->d_sb, compat_ptr(arg));
+}
+#endif
+
+/* ---------------------------------------------------------------------- */
+
 void sysaufs_br_init(struct au_branch *br)
 {
 	int i;

include/uapi/linux/aufs_type.h

@@ -193,7 +193,8 @@ static inline int au_br_wh_linkable(int brperm)
 
 /* ioctl */
 enum {
-	AuCtl_WBR_FD	/* pathconf wrapper */
+	AuCtl_WBR_FD,	/* pathconf wrapper */
+	AuCtl_BR	/* info about branches */
 };
 
 /* borrowed from linux/include/linux/kernel.h */
@@ -243,8 +244,21 @@ struct aufs_wbr_fd {
 
 /* ---------------------------------------------------------------------- */
 
+union aufs_brinfo {
+	/* PATH_MAX may differ between kernel-space and user-space */
+	char	_spacer[4096];
+	struct {
+		int16_t	id;
+		int	perm;
+		char	path[0];
+	};
+} __aligned(8);
+
+/* ---------------------------------------------------------------------- */
+
 #define AuCtlType		'A'
 #define AUFS_CTL_WBR_FD		_IOW(AuCtlType, AuCtl_WBR_FD, \
 				     struct aufs_wbr_fd)
+#define AUFS_CTL_BRINFO		_IOW(AuCtlType, AuCtl_BR, union aufs_brinfo)
 
 #endif /* __AUFS_TYPE_H__ */