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Subject[PATCH 05/20] afs: Implement @sys substitution handling
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Date
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>
---

Documentation/filesystems/afs.txt | 28 +++++
fs/afs/dir.c | 78 ++++++++++++++
fs/afs/internal.h | 13 ++
fs/afs/main.c | 42 +++++++
fs/afs/proc.c | 211 +++++++++++++++++++++++++++++++++++++
5 files changed, 369 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/afs.txt b/Documentation/filesystems/afs.txt
index c5254f6d234d..8c6ea7b41048 100644
--- a/Documentation/filesystems/afs.txt
+++ b/Documentation/filesystems/afs.txt
@@ -11,7 +11,7 @@ Contents:
- Proc filesystem.
- The cell database.
- Security.
- - Examples.
+ - The @sys substitution.


========
@@ -230,3 +230,29 @@ If a file is opened with a particular key and then the file descriptor is
passed to a process that doesn't have that key (perhaps over an AF_UNIX
socket), then the operations on the file will be made with key that was used to
open the file.
+
+
+=====================
+THE @SYS SUBSTITUTION
+=====================
+
+The list of up to 16 @sys substitutions for the current network namespace can
+be configured by writing a list to /proc/fs/afs/sysname:
+
+ [root@andromeda ~]# echo foo amd64_linux_26 >/proc/fs/afs/sysname
+
+or cleared entirely by writing an empty list:
+
+ [root@andromeda ~]# echo >/proc/fs/afs/sysname
+
+The current list for current network namespace can be retrieved by:
+
+ [root@andromeda ~]# cat /proc/fs/afs/sysname
+ foo
+ amd64_linux_26
+
+When @sys is being substituted for, each element of the list is tried in the
+order given.
+
+By default, the list will contain one item that conforms to the pattern
+"<arch>_linux_26", amd64 being the name for x86_64.
diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 63f7b37e1e71..9bac606725ee 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -589,7 +589,7 @@ static struct inode *afs_do_lookup(struct inode *dir, struct dentry *dentry,
inode = ilookup5(dir->i_sb, cookie->fids[0].vnode, afs_iget5_test, &data);
if (inode)
goto out;
-
+
/* Need space for examining all the selected files */
inode = ERR_PTR(-ENOMEM);
cookie->statuses = kcalloc(cookie->nr_fids, sizeof(struct afs_file_status),
@@ -766,6 +766,75 @@ static struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir
return ERR_PTR(ret);
}

+/*
+ * Look up an entry in a directory with @sys substitution.
+ */
+static struct dentry *afs_lookup_atsys(struct inode *dir, struct dentry *dentry,
+ struct key *key)
+{
+ struct afs_sysnames *subs;
+ struct afs_net *net = afs_i2net(dir);
+ struct dentry *parent, *ret;
+ char *buf, *p, *name;
+ int len, i;
+
+ _enter("");
+
+ parent = dget_parent(dentry);
+
+ ret = ERR_PTR(-ENOMEM);
+ p = buf = kmalloc(AFSNAMEMAX, GFP_KERNEL);
+ if (!buf)
+ goto out_p;
+ if (dentry->d_name.len > 4) {
+ memcpy(p, dentry->d_name.name, dentry->d_name.len - 4);
+ p += dentry->d_name.len - 4;
+ }
+
+ /* There is an ordered list of substitutes that we have to try */
+ for (i = 0; i < AFS_NR_SYSNAME; i++) {
+ read_lock(&net->sysnames_lock);
+ subs = net->sysnames;
+ if (!subs || i >= subs->nr) {
+ read_unlock(&net->sysnames_lock);
+ goto noent;
+ }
+
+ name = subs->subs[i];
+ if (!name) {
+ read_unlock(&net->sysnames_lock);
+ goto noent;
+ }
+
+ len = dentry->d_name.len - 4 + strlen(name);
+ if (len >= AFSNAMEMAX) {
+ read_unlock(&net->sysnames_lock);
+ ret = ERR_PTR(-ENAMETOOLONG);
+ goto out_b;
+ }
+
+ strcpy(p, name);
+ read_unlock(&net->sysnames_lock);
+
+ ret = lookup_one_len(buf, parent, len);
+ if (IS_ERR(ret) || d_is_positive(ret))
+ goto out_b;
+ dput(ret);
+ }
+
+noent:
+ /* We don't want to d_add() the @sys dentry here as we don't want to
+ * the cached dentry to hide changes to the sysnames list.
+ */
+ ret = NULL;
+out_b:
+ kfree(buf);
+out_p:
+ dput(parent);
+ key_put(key);
+ return ret;
+}
+
/*
* look up an entry in a directory
*/
@@ -805,6 +874,13 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
return ERR_PTR(ret);
}

+ if (dentry->d_name.len >= 4 &&
+ dentry->d_name.name[dentry->d_name.len - 4] == '@' &&
+ dentry->d_name.name[dentry->d_name.len - 3] == 's' &&
+ dentry->d_name.name[dentry->d_name.len - 2] == 'y' &&
+ dentry->d_name.name[dentry->d_name.len - 1] == 's')
+ return afs_lookup_atsys(dir, dentry, key);
+
inode = afs_do_lookup(dir, dentry, key);
if (IS_ERR(inode)) {
ret = PTR_ERR(inode);
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index 55b07e818400..c584d6e4c2f5 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -198,6 +198,16 @@ 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];
+ unsigned short nr;
+ short error;
+};
+
/*
* AFS network namespace record.
*/
@@ -246,8 +256,11 @@ 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 {
diff --git a/fs/afs/main.c b/fs/afs/main.c
index 15a02a05ff40..01a55d25d064 100644
--- a/fs/afs/main.c
+++ b/fs/afs/main.c
@@ -34,11 +34,42 @@ MODULE_PARM_DESC(rootcell, "root AFS cell name and VL server IP addr list");
struct workqueue_struct *afs_wq;
struct afs_net __afs_net;

+#if defined(CONFIG_ALPHA)
+const char afs_init_sysname[] = "alpha_linux26";
+#elif defined(CONFIG_X86_64)
+const char afs_init_sysname[] = "amd64_linux26";
+#elif defined(CONFIG_ARM)
+const char afs_init_sysname[] = "arm_linux26";
+#elif defined(CONFIG_ARM64)
+const char afs_init_sysname[] = "aarch64_linux26";
+#elif defined(CONFIG_X86_32)
+const char afs_init_sysname[] = "i386_linux26";
+#elif defined(CONFIG_IA64)
+const char afs_init_sysname[] = "ia64_linux26";
+#elif defined(CONFIG_PPC64)
+const char afs_init_sysname[] = "ppc64_linux26";
+#elif defined(CONFIG_PPC32)
+const char afs_init_sysname[] = "ppc_linux26";
+#elif defined(CONFIG_S390)
+#ifdef CONFIG_64BIT
+const char afs_init_sysname[] = "s390x_linux26";
+#else
+const char afs_init_sysname[] = "s390_linux26";
+#endif
+#elif defined(CONFIG_SPARC64)
+const char afs_init_sysname[] = "sparc64_linux26";
+#elif defined(CONFIG_SPARC32)
+const char afs_init_sysname[] = "sparc_linux26";
+#else
+const char afs_init_sysname[] = "unknown_linux26";
+#endif
+
/*
* Initialise an AFS network namespace record.
*/
static int __net_init afs_net_init(struct afs_net *net)
{
+ struct afs_sysnames *sysnames;
int ret;

net->live = true;
@@ -67,6 +98,15 @@ static int __net_init afs_net_init(struct afs_net *net)
INIT_WORK(&net->fs_manager, afs_manage_servers);
timer_setup(&net->fs_timer, afs_servers_timer, 0);

+ ret = -ENOMEM;
+ sysnames = kzalloc(sizeof(*sysnames), GFP_KERNEL);
+ if (!sysnames)
+ goto error_sysnames;
+ sysnames->subs[0] = (char *)&afs_init_sysname;
+ sysnames->nr = 1;
+ net->sysnames = sysnames;
+ rwlock_init(&net->sysnames_lock);
+
/* Register the /proc stuff */
ret = afs_proc_init(net);
if (ret < 0)
@@ -92,6 +132,8 @@ static int __net_init afs_net_init(struct afs_net *net)
net->live = false;
afs_proc_cleanup(net);
error_proc:
+ kfree(net->sysnames);
+error_sysnames:
net->live = false;
return ret;
}
diff --git a/fs/afs/proc.c b/fs/afs/proc.c
index 2f04d37eeef0..7e9d6b2f9734 100644
--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -126,6 +126,32 @@ static const struct file_operations afs_proc_servers_fops = {
.release = seq_release,
};

+static int afs_proc_sysname_open(struct inode *inode, struct file *file);
+static int afs_proc_sysname_release(struct inode *inode, struct file *file);
+static void *afs_proc_sysname_start(struct seq_file *p, loff_t *pos);
+static void *afs_proc_sysname_next(struct seq_file *p, void *v,
+ loff_t *pos);
+static void afs_proc_sysname_stop(struct seq_file *p, void *v);
+static int afs_proc_sysname_show(struct seq_file *m, void *v);
+static ssize_t afs_proc_sysname_write(struct file *file,
+ const char __user *buf,
+ size_t size, loff_t *_pos);
+
+static const struct seq_operations afs_proc_sysname_ops = {
+ .start = afs_proc_sysname_start,
+ .next = afs_proc_sysname_next,
+ .stop = afs_proc_sysname_stop,
+ .show = afs_proc_sysname_show,
+};
+
+static const struct file_operations afs_proc_sysname_fops = {
+ .open = afs_proc_sysname_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = afs_proc_sysname_release,
+ .write = afs_proc_sysname_write,
+};
+
/*
* initialise the /proc/fs/afs/ directory
*/
@@ -139,7 +165,8 @@ int afs_proc_init(struct afs_net *net)

if (!proc_create("cells", 0644, net->proc_afs, &afs_proc_cells_fops) ||
!proc_create("rootcell", 0644, net->proc_afs, &afs_proc_rootcell_fops) ||
- !proc_create("servers", 0644, net->proc_afs, &afs_proc_servers_fops))
+ !proc_create("servers", 0644, net->proc_afs, &afs_proc_servers_fops) ||
+ !proc_create("sysname", 0644, net->proc_afs, &afs_proc_sysname_fops))
goto error_tree;

_leave(" = 0");
@@ -635,3 +662,185 @@ static int afs_proc_servers_show(struct seq_file *m, void *v)
&alist->addrs[alist->index].transport);
return 0;
}
+
+static void afs_sysnames_free(struct afs_sysnames *sysnames)
+{
+ int i;
+
+ if (sysnames) {
+ for (i = 0; i < sysnames->nr; i++)
+ if (sysnames->subs[i] != afs_init_sysname)
+ kfree(sysnames->subs[i]);
+ }
+}
+
+/*
+ * Handle opening of /proc/fs/afs/sysname. If it is opened for writing, we
+ * assume the caller wants to change the substitution list and we allocate a
+ * buffer to hold the list.
+ */
+static int afs_proc_sysname_open(struct inode *inode, struct file *file)
+{
+ struct afs_sysnames *sysnames;
+ struct seq_file *m;
+ int ret;
+
+ ret = seq_open(file, &afs_proc_sysname_ops);
+ if (ret < 0)
+ return ret;
+
+ if (file->f_mode & FMODE_WRITE) {
+ sysnames = kzalloc(sizeof(*sysnames), GFP_KERNEL);
+ if (!sysnames) {
+ seq_release(inode, file);
+ return -ENOMEM;
+ }
+
+ m = file->private_data;
+ m->private = sysnames;
+ }
+
+ return 0;
+}
+
+/*
+ * Handle writes to /proc/fs/afs/sysname to set the @sys substitution.
+ */
+static ssize_t afs_proc_sysname_write(struct file *file,
+ const char __user *buf,
+ size_t size, loff_t *_pos)
+{
+ struct afs_sysnames *sysnames;
+ struct seq_file *m = file->private_data;
+ char *kbuf = NULL, *s, *p, *sub;
+ int ret, len;
+
+ sysnames = m->private;
+ if (!sysnames)
+ return -EINVAL;
+ if (sysnames->error)
+ return sysnames->error;
+
+ if (size >= PAGE_SIZE - 1) {
+ sysnames->error = -EINVAL;
+ return -EINVAL;
+ }
+ if (size == 0)
+ return 0;
+
+ kbuf = memdup_user_nul(buf, size);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ inode_lock(file_inode(file));
+
+ p = kbuf;
+ while ((s = strsep(&p, " \t\n"))) {
+ len = strlen(s);
+ if (len == 0)
+ continue;
+ if (len >= AFSNAMEMAX) {
+ sysnames->error = -ENAMETOOLONG;
+ ret = -ENAMETOOLONG;
+ goto out;
+ }
+ if (len >= 4 &&
+ s[len - 4] == '@' &&
+ s[len - 3] == 's' &&
+ s[len - 2] == 'y' &&
+ s[len - 1] == 's') {
+ /* Protect against recursion */
+ sysnames->error = -EINVAL;
+ ret = -EINVAL;
+ goto out;
+ }
+
+ if (sysnames->nr >= AFS_NR_SYSNAME) {
+ sysnames->error = -EFBIG;
+ ret = -EFBIG;
+ goto out;
+ }
+
+ if (strcmp(s, afs_init_sysname) == 0) {
+ sub = (char *)afs_init_sysname;
+ } else {
+ ret = -ENOMEM;
+ sub = kmemdup(s, len + 1, GFP_KERNEL);
+ if (!sub)
+ goto out;
+ }
+
+ sysnames->subs[sysnames->nr] = sub;
+ sysnames->nr++;
+ }
+
+ ret = size; /* consume everything, always */
+out:
+ inode_unlock(file_inode(file));
+ kfree(kbuf);
+ return ret;
+}
+
+static int afs_proc_sysname_release(struct inode *inode, struct file *file)
+{
+ struct afs_sysnames *sysnames, *kill = NULL;
+ struct seq_file *m = file->private_data;
+ struct afs_net *net = afs_seq2net(m);
+
+ sysnames = m->private;
+ if (sysnames) {
+ kill = sysnames;
+ if (!sysnames->error) {
+ write_lock(&net->sysnames_lock);
+ kill = net->sysnames;
+ net->sysnames = sysnames;
+ write_unlock(&net->sysnames_lock);
+ }
+ afs_sysnames_free(kill);
+ }
+
+ return seq_release(inode, file);
+}
+
+static void *afs_proc_sysname_start(struct seq_file *m, loff_t *pos)
+ __acquires(&net->sysnames_lock)
+{
+ struct afs_net *net = afs_seq2net(m);
+ struct afs_sysnames *names = net->sysnames;
+
+ read_lock(&net->sysnames_lock);
+
+ if (*pos >= names->nr)
+ return NULL;
+ return (void *)(unsigned long)(*pos + 1);
+}
+
+static void *afs_proc_sysname_next(struct seq_file *m, void *v, loff_t *pos)
+{
+ struct afs_net *net = afs_seq2net(m);
+ struct afs_sysnames *names = net->sysnames;
+
+ *pos += 1;
+ if (*pos >= names->nr)
+ return NULL;
+ return (void *)(unsigned long)(*pos + 1);
+}
+
+static void afs_proc_sysname_stop(struct seq_file *m, void *v)
+ __releases(&net->sysnames_lock)
+{
+ struct afs_net *net = afs_seq2net(m);
+
+ read_unlock(&net->sysnames_lock);
+}
+
+static int afs_proc_sysname_show(struct seq_file *m, void *v)
+{
+ struct afs_net *net = afs_seq2net(m);
+ struct afs_sysnames *sysnames = net->sysnames;
+ unsigned int i = (unsigned long)v - 1;
+
+ if (i < sysnames->nr)
+ seq_printf(m, "%s\n", sysnames->subs[i]);
+ return 0;
+}
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