libfs: allow error return from simple attributes

Sometimes simple attributes might need to return an error, e.g. for
acquiring a mutex interruptibly.  In fact we have that situation in
spufs already which is the original user of the simple attributes.  This
patch merged the temporarily forked attributes in spufs back into the
main ones and allows to return errors.

[akpm@linux-foundation.org: build fix]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: <stefano.brivio@polimi.it>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg KH <greg@kroah.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 33 insertions, 20 deletions

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index fa6b7f7ff914..fddffe4851f5 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -56,13 +56,15 @@ const struct inode_operations debugfs_link_operations = {
         .follow_link    = debugfs_follow_link,
 };
 
-static void debugfs_u8_set(void *data, u64 val)
+static int debugfs_u8_set(void *data, u64 val)
 {
         *(u8 *)data = val;
+        return 0;
 }
-static u64 debugfs_u8_get(void *data)
+static int debugfs_u8_get(void *data, u64 *val)
 {
-        return *(u8 *)data;
+        *val = *(u8 *)data;
+        return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u8, debugfs_u8_get, debugfs_u8_set, "%llu\n");
 
@@ -97,13 +99,15 @@ struct dentry *debugfs_create_u8(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u8);
 
-static void debugfs_u16_set(void *data, u64 val)
+static int debugfs_u16_set(void *data, u64 val)
 {
         *(u16 *)data = val;
+        return 0;
 }
-static u64 debugfs_u16_get(void *data)
+static int debugfs_u16_get(void *data, u64 *val)
 {
-        return *(u16 *)data;
+        *val = *(u16 *)data;
+        return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u16, debugfs_u16_get, debugfs_u16_set, "%llu\n");
 
@@ -138,13 +142,15 @@ struct dentry *debugfs_create_u16(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u16);
 
-static void debugfs_u32_set(void *data, u64 val)
+static int debugfs_u32_set(void *data, u64 val)
 {
         *(u32 *)data = val;
+        return 0;
 }
-static u64 debugfs_u32_get(void *data)
+static int debugfs_u32_get(void *data, u64 *val)
 {
-        return *(u32 *)data;
+        *val = *(u32 *)data;
+        return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u32, debugfs_u32_get, debugfs_u32_set, "%llu\n");
 
@@ -179,14 +185,16 @@ struct dentry *debugfs_create_u32(const char *name, mode_t mode,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_u32);
 
-static void debugfs_u64_set(void *data, u64 val)
+static int debugfs_u64_set(void *data, u64 val)
 {
         *(u64 *)data = val;
+        return 0;
 }
 
-static u64 debugfs_u64_get(void *data)
+static int debugfs_u64_get(void *data, u64 *val)
 {
-        return *(u64 *)data;
+        *val = *(u64 *)data;
+        return 0;
 }
 DEFINE_SIMPLE_ATTRIBUTE(fops_u64, debugfs_u64_get, debugfs_u64_set, "%llu\n");
 
diff --git a/fs/libfs.c b/fs/libfs.c
index 5523bde96387..2319415ddb5e 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -583,8 +583,8 @@ int simple_transaction_release(struct inode *inode, struct file *file)
 /* Simple attribute files */
 
 struct simple_attr {
-        u64 (*get)(void *);
-        void (*set)(void *, u64);
+        int (*get)(void *, u64 *);
+        int (*set)(void *, u64);
         char get_buf[24];       /* enough to store a u64 and "\n\0" */
         char set_buf[24];
         void *data;
@@ -595,7 +595,7 @@ struct simple_attr {
 /* simple_attr_open is called by an actual attribute open file operation
  * to set the attribute specific access operations. */
 int simple_attr_open(struct inode *inode, struct file *file,
-                     u64 (*get)(void *), void (*set)(void *, u64),
+                     int (*get)(void *, u64 *), int (*set)(void *, u64),
                      const char *fmt)
 {
         struct simple_attr *attr;
@@ -635,14 +635,20 @@ ssize_t simple_attr_read(struct file *file, char __user *buf,
                 return -EACCES;
 
         mutex_lock(&attr->mutex);
-        if (*ppos) /* continued read */
+        if (*ppos) {            /* continued read */
                 size = strlen(attr->get_buf);
-        else      /* first read */
+        } else {                /* first read */
+                u64 val;
+                ret = attr->get(attr->data, &val);
+                if (ret)
+                        goto out;
+
                 size = scnprintf(attr->get_buf, sizeof(attr->get_buf),
-                                 attr->fmt,
-                                 (unsigned long long)attr->get(attr->data));
+                                 attr->fmt, (unsigned long long)val);
+        }
 
         ret = simple_read_from_buffer(buf, len, ppos, attr->get_buf, size);
+out:
         mutex_unlock(&attr->mutex);
         return ret;
 }
@@ -657,7 +663,6 @@ ssize_t simple_attr_write(struct file *file, const char __user *buf,
         ssize_t ret;
 
         attr = file->private_data;
-
         if (!attr->set)
                 return -EACCES;