[PATCH] simple_read_buffer() helper function

A number of drivers or special virtual devices really just want their
"read()" function to populate user space from some internal buffer.

This adds such a helper function - "simple_read_from_buffer()" - and
converts several ->read() instances to use it.
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ia64/kernel/salinfo.c

@@ -426,8 +426,6 @@ salinfo_log_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
 	struct inode *inode = file->f_dentry->d_inode;
 	struct proc_dir_entry *entry = PDE(inode);
 	struct salinfo_data *data = entry->data;
-	void *saldata;
-	size_t size;
 	u8 *buf;
 	u64 bufsize;
 
@@ -441,18 +439,7 @@ salinfo_log_read(struct file *file, char *buffer, size_t count, loff_t *ppos)
 		buf = NULL;
 		bufsize = 0;
 	}
-	if (*ppos >= bufsize)
-		return 0;
-
-	saldata = buf + file->f_pos;
-	size = bufsize - file->f_pos;
-	if (size > count)
-		size = count;
-	if (copy_to_user(buffer, saldata, size))
-		return -EFAULT;
-
-	*ppos += size;
-	return size;
+	return simple_read_from_buffer(buffer, count, ppos, buf, bufsize);
 }
 
 static void

arch/ppc64/kernel/proc_ppc64.c

@@ -161,21 +161,10 @@ static loff_t page_map_seek( struct file *file, loff_t off, int whence)
 	return (file->f_pos = new);
 }
 
-static ssize_t page_map_read( struct file *file, char *buf, size_t nbytes, loff_t *ppos)
+static ssize_t page_map_read( struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
 {
-	unsigned pos = *ppos;
 	struct proc_dir_entry *dp = PDE(file->f_dentry->d_inode);
-
-	if ( pos >= dp->size )
-		return 0;
-	if ( nbytes >= dp->size )
-		nbytes = dp->size;
-	if ( pos + nbytes > dp->size )
-		nbytes = dp->size - pos;
-
-	copy_to_user( buf, (char *)dp->data + pos, nbytes );
-	*ppos = pos + nbytes;
-	return nbytes;
+	return simple_read_from_buffer(buf, nbytes, ppos, dp->data, dp->size);
 }
 
 static int page_map_mmap( struct file *file, struct vm_area_struct *vma )

drivers/acpi/system.c

@@ -92,8 +92,7 @@ acpi_system_read_dsdt (
 {
 	acpi_status		status = AE_OK;
 	struct acpi_buffer	dsdt = {ACPI_ALLOCATE_BUFFER, NULL};
-	void			*data = NULL;
-	size_t			size = 0;
+	ssize_t			res;
 
 	ACPI_FUNCTION_TRACE("acpi_system_read_dsdt");
 
@@ -101,22 +100,11 @@ acpi_system_read_dsdt (
 	if (ACPI_FAILURE(status))
 		return_VALUE(-ENODEV);
 
-	if (*ppos < dsdt.length) {
-		data = dsdt.pointer + file->f_pos;
-		size = dsdt.length - file->f_pos;
-		if (size > count)
-			size = count;
-		if (copy_to_user(buffer, data, size)) {
-			acpi_os_free(dsdt.pointer);
-			return_VALUE(-EFAULT);
-		}
-	}
-
+	res = simple_read_from_buffer(buffer, count, ppos,
+				      dsdt.pointer, dsdt.length);
 	acpi_os_free(dsdt.pointer);
 
-	*ppos += size;
-
-	return_VALUE(size);
+	return_VALUE(res);
 }
 
 
@@ -135,8 +123,7 @@ acpi_system_read_fadt (
 {
 	acpi_status		status = AE_OK;
 	struct acpi_buffer	fadt = {ACPI_ALLOCATE_BUFFER, NULL};
-	void			*data = NULL;
-	size_t			size = 0;
+	ssize_t			res;
 
 	ACPI_FUNCTION_TRACE("acpi_system_read_fadt");
 
@@ -144,22 +131,11 @@ acpi_system_read_fadt (
 	if (ACPI_FAILURE(status))
 		return_VALUE(-ENODEV);
 
-	if (*ppos < fadt.length) {
-		data = fadt.pointer + file->f_pos;
-		size = fadt.length - file->f_pos;
-		if (size > count)
-			size = count;
-		if (copy_to_user(buffer, data, size)) {
-			acpi_os_free(fadt.pointer);
-			return_VALUE(-EFAULT);
-		}
-	}
-
+	res = simple_read_from_buffer(buffer, count, ppos,
+				      fadt.pointer, fadt.length);
 	acpi_os_free(fadt.pointer);
 
-	*ppos += size;
-
-	return_VALUE(size);
+	return_VALUE(res);
 }
 
 

drivers/oprofile/oprofilefs.c

@@ -47,23 +47,7 @@ static struct super_operations s_ops = {
 
 ssize_t oprofilefs_str_to_user(char const * str, char __user * buf, size_t count, loff_t * offset)
 {
-	size_t len = strlen(str);
-
-	if (!count)
-		return 0;
-
-	if (*offset > len)
-		return 0;
-
-	if (count > len - *offset)
-		count = len - *offset;
-
-	if (copy_to_user(buf, str + *offset, count))
-		return -EFAULT;
-
-	*offset += count;
-
-	return count;
+	return simple_read_from_buffer(buf, count, offset, str, strlen(str));
 }
 
 
@@ -72,29 +56,10 @@ ssize_t oprofilefs_str_to_user(char const * str, char __user * buf, size_t count
 ssize_t oprofilefs_ulong_to_user(unsigned long val, char __user * buf, size_t count, loff_t * offset)
 {
 	char tmpbuf[TMPBUFSIZE];
-	size_t maxlen;
-
-	if (!count)
-		return 0;
-
-	spin_lock(&oprofilefs_lock);
-	maxlen = snprintf(tmpbuf, TMPBUFSIZE, "%lu\n", val);
-	spin_unlock(&oprofilefs_lock);
+	size_t maxlen = snprintf(tmpbuf, TMPBUFSIZE, "%lu\n", val);
 	if (maxlen > TMPBUFSIZE)
 		maxlen = TMPBUFSIZE;
-
-	if (*offset > maxlen)
-		return 0;
-
-	if (count > maxlen - *offset)
-		count = maxlen - *offset;
-
-	if (copy_to_user(buf, tmpbuf + *offset, count))
-		return -EFAULT;
-
-	*offset += count;
-
-	return count;
+	return simple_read_from_buffer(buf, count, offset, tmpbuf, maxlen);
 }
 
 

drivers/usb/host/uhci-debug.c

@@ -571,22 +571,7 @@ static ssize_t uhci_proc_read(struct file *file, char __user *buf,
 				size_t nbytes, loff_t *ppos)
 {
 	struct uhci_proc *up = file->private_data;
-	unsigned int pos;
-	unsigned int size;
-
-	pos = *ppos;
-	size = up->size;
-	if (pos >= size)
-		return 0;
-	if (nbytes > size - pos)
-		nbytes = size - pos;
-
-	if (copy_to_user(buf, up->data + pos, nbytes))
-		return -EFAULT;
-
-	*ppos += nbytes;
-
-	return nbytes;
+	return simple_read_from_buffer(buf, nbytes, ppos, up->data, up->size);
 }
 
 static int uhci_proc_release(struct inode *inode, struct file *file)

fs/libfs.c

@@ -7,6 +7,7 @@
 #include <linux/pagemap.h>
 #include <linux/mount.h>
 #include <linux/vfs.h>
+#include <asm/uaccess.h>
 
 int simple_getattr(struct vfsmount *mnt, struct dentry *dentry,
 		   struct kstat *stat)
@@ -439,6 +440,22 @@ void simple_release_fs(struct vfsmount **mount, int *count)
 	mntput(mnt);
 }
 
+ssize_t simple_read_from_buffer(void __user *to, size_t count, loff_t *ppos,
+				void *from, size_t available)
+{
+	loff_t pos = *ppos;
+	if (pos < 0)
+		return -EINVAL;
+	if (pos >= available)
+		return 0;
+	if (count > available - pos)
+		count = available - pos;
+	if (copy_to_user(to, from + pos, count))
+		return -EFAULT;
+	*ppos = pos + count;
+	return count;
+}
+
 EXPORT_SYMBOL(dcache_dir_close);
 EXPORT_SYMBOL(dcache_dir_lseek);
 EXPORT_SYMBOL(dcache_dir_open);
@@ -461,3 +478,4 @@ EXPORT_SYMBOL(simple_rmdir);
 EXPORT_SYMBOL(simple_statfs);
 EXPORT_SYMBOL(simple_sync_file);
 EXPORT_SYMBOL(simple_unlink);
+EXPORT_SYMBOL(simple_read_from_buffer);

include/linux/fs.h

@@ -1527,6 +1527,8 @@ extern int simple_fill_super(struct super_block *, int, struct tree_descr *);
 extern int simple_pin_fs(char *name, struct vfsmount **mount, int *count);
 extern void simple_release_fs(struct vfsmount **mount, int *count);
 
+extern ssize_t simple_read_from_buffer(void __user *, size_t, loff_t *, void *, size_t);
+
 extern int inode_change_ok(struct inode *, struct iattr *);
 extern int __must_check inode_setattr(struct inode *, struct iattr *);