afs: Implement @sys substitution handling

Implement the AFS feature by which @sys at the end of a pathname component
may be substituted for one of a list of values, typically naming the
operating system.  Up to 16 alternatives may be specified and these are
tried in turn until one works.  Each network namespace has[*] a separate
independent list.

Upon creation of a new network namespace, the list of values is
initialised[*] to a single OpenAFS-compatible string representing arch type
plus "_linux26".  For example, on x86_64, the sysname is "amd64_linux26".

[*] Or will, once network namespace support is finalised in kAFS.

The list may be set by:

	# for i in foo bar linux-x86_64; do echo $i; done >/proc/fs/afs/sysname

for which separate writes to the same fd are amalgamated and applied on
close.  The LF character may be used as a separator to specify multiple
items in the same write() call.

The list may be cleared by:

	# echo >/proc/fs/afs/sysname

and read by:

	# cat /proc/fs/afs/sysname
	foo
	bar
	linux-x86_64

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 55b07e818400..27150bbc50d8 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -199,6 +199,18 @@ static inline struct afs_super_info *AFS_FS_S(struct super_block *sb)
 extern struct file_system_type afs_fs_type;
 
 /*
+ * Set of substitutes for @sys.
+ */
+struct afs_sysnames {
+#define AFS_NR_SYSNAME 16
+	char			*subs[AFS_NR_SYSNAME];
+	refcount_t		usage;
+	unsigned short		nr;
+	short			error;
+	char			blank[1];
+};
+
+/*
  * AFS network namespace record.
  */
 struct afs_net {
@@ -246,8 +258,11 @@ struct afs_net {
 
 	/* Misc */
 	struct proc_dir_entry	*proc_afs;		/* /proc/net/afs directory */
+	struct afs_sysnames	*sysnames;
+	rwlock_t		sysnames_lock;
 };
 
+extern const char afs_init_sysname[];
 extern struct afs_net __afs_net;// Dummy AFS network namespace; TODO: replace with real netns
 
 enum afs_cell_state {
@@ -789,6 +804,7 @@ extern int __net_init afs_proc_init(struct afs_net *);
 extern void __net_exit afs_proc_cleanup(struct afs_net *);
 extern int afs_proc_cell_setup(struct afs_net *, struct afs_cell *);
 extern void afs_proc_cell_remove(struct afs_net *, struct afs_cell *);
+extern void afs_put_sysnames(struct afs_sysnames *);
 
 /*
  * rotate.c