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[RFC v4 09/25] char/nvram: Implement NVRAM read/write methods

From Finn Thain <fthain@telegraphics.com.au>
Newsgroups linux.kernel
Subject [RFC v4 09/25] char/nvram: Implement NVRAM read/write methods
Date 2015-07-12 12:50 +0200
Message-ID <pLmZB-7cl-31@gated-at.bofh.it> (permalink)
References <pLmZz-7cl-3@gated-at.bofh.it>
Organization linux.* mail to news gateway

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Refactor the RTC "CMOS" NVRAM functions so that they can be used as
arch_nvram_ops methods. Checksumming logic is moved from the misc device
operations to the nvram read/write operations.

This makes the misc device implementation more generic. This also
preserves the locking semantics such that "read if checksum valid" and
"write and update checksum" remain atomic operations.

PPC64 implements byte-range read/write methods which are similar to
file_operations struct methods. Other platforms provide only
byte-at-a-time functions. So the misc device prefers the former but
will fall back on the latter.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>

---
 drivers/char/nvram.c |  162 +++++++++++++++++++++++++++++++++++----------------
 1 file changed, 114 insertions(+), 48 deletions(-)

Index: linux/drivers/char/nvram.c
===================================================================
--- linux.orig/drivers/char/nvram.c	2015-07-12 20:25:02.000000000 +1000
+++ linux/drivers/char/nvram.c	2015-07-12 20:25:03.000000000 +1000
@@ -41,6 +41,7 @@
 #include <linux/init.h>
 #include <linux/proc_fs.h>
 #include <linux/seq_file.h>
+#include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/io.h>
 #include <linux/uaccess.h>
@@ -178,9 +179,48 @@ static ssize_t nvram_get_size(void)
 	return NVRAM_BYTES;
 }
 
+static ssize_t nvram_read(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		*p = __nvram_read_byte(i);
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
+static ssize_t nvram_write(char *buf, size_t count, loff_t *ppos)
+{
+	char *p = buf;
+	loff_t i;
+
+	spin_lock_irq(&rtc_lock);
+	if (!__nvram_check_checksum()) {
+		spin_unlock_irq(&rtc_lock);
+		return -EIO;
+	}
+	for (i = *ppos; count > 0 && i < NVRAM_BYTES; --count, ++i, ++p)
+		__nvram_write_byte(*p, i);
+	__nvram_set_checksum();
+	spin_unlock_irq(&rtc_lock);
+
+	*ppos = i;
+	return p - buf;
+}
+
 const struct nvram_ops arch_nvram_ops = {
 	.read_byte      = nvram_read_byte,
 	.write_byte     = nvram_write_byte,
+	.read           = nvram_read,
+	.write          = nvram_write,
 	.get_size       = nvram_get_size,
 	.set_checksum   = nvram_set_checksum,
 	.initialize     = nvram_initialize,
@@ -215,69 +255,95 @@ static loff_t nvram_misc_llseek(struct f
 static ssize_t nvram_misc_read(struct file *file, char __user *buf,
                                size_t count, loff_t *ppos)
 {
-	unsigned char contents[NVRAM_BYTES];
-	unsigned i = *ppos;
-	unsigned char *tmp;
-
-	spin_lock_irq(&rtc_lock);
+	loff_t i;
+	char __user *p = buf;
 
-	if (!__nvram_check_checksum())
-		goto checksum_err;
-
-	for (tmp = contents; count-- > 0 && i < NVRAM_BYTES; ++i, ++tmp)
-		*tmp = __nvram_read_byte(i);
-
-	spin_unlock_irq(&rtc_lock);
-
-	if (copy_to_user(buf, contents, tmp - contents))
+	if (!access_ok(VERIFY_WRITE, buf, count))
 		return -EFAULT;
+	if (*ppos >= nvram_size)
+		return 0;
 
-	*ppos = i;
-
-	return tmp - contents;
+	/* If the arch provided a byte range read op, use it. Otherwise
+	 * fall back on the byte-at-a-time accessor.
+	 */
+	if (arch_nvram_ops.read != NULL) {
+		char *tmp;
+		ssize_t ret;
+
+		count = min_t(size_t, count, nvram_size - *ppos);
+		count = min_t(size_t, count, PAGE_SIZE);
+
+		tmp = kmalloc(count, GFP_KERNEL);
+		if (!tmp)
+			return -ENOMEM;
+
+		ret = arch_nvram_ops.read(tmp, count, ppos);
+		if (ret <= 0)
+			goto out;
+
+		if (copy_to_user(buf, tmp, ret)) {
+			*ppos -= ret;
+			ret = -EFAULT;
+		}
+
+out:
+		kfree(tmp);
+		return ret;
+	}
 
-checksum_err:
-	spin_unlock_irq(&rtc_lock);
-	return -EIO;
+	for (i = *ppos; count > 0 && i < nvram_size; ++i, ++p, --count)
+		if (__put_user(arch_nvram_ops.read_byte(i), p))
+			return -EFAULT;
+	*ppos = i;
+	return p - buf;
 }
 
 static ssize_t nvram_misc_write(struct file *file, const char __user *buf,
                                 size_t count, loff_t *ppos)
 {
-	unsigned char contents[NVRAM_BYTES];
-	unsigned i = *ppos;
-	unsigned char *tmp;
-
-	if (i >= NVRAM_BYTES)
-		return 0;	/* Past EOF */
-
-	if (count > NVRAM_BYTES - i)
-		count = NVRAM_BYTES - i;
-	if (count > NVRAM_BYTES)
-		return -EFAULT;	/* Can't happen, but prove it to gcc */
+	loff_t i;
+	const char __user *p = buf;
 
-	if (copy_from_user(contents, buf, count))
+	if (!access_ok(VERIFY_READ, buf, count))
 		return -EFAULT;
+	if (*ppos >= nvram_size)
+		return 0;
 
-	spin_lock_irq(&rtc_lock);
-
-	if (!__nvram_check_checksum())
-		goto checksum_err;
-
-	for (tmp = contents; count--; ++i, ++tmp)
-		__nvram_write_byte(*tmp, i);
-
-	__nvram_set_checksum();
+	/* If the arch provided a byte range write op, use it. Otherwise
+	 * fall back on the byte-at-a-time accessor.
+	 */
+	if (arch_nvram_ops.write != NULL) {
+		char *tmp;
+		ssize_t ret;
+
+		count = min_t(size_t, count, nvram_size - *ppos);
+		count = min_t(size_t, count, PAGE_SIZE);
+
+		tmp = kmalloc(count, GFP_KERNEL);
+		if (!tmp)
+			return -ENOMEM;
+
+		if (copy_from_user(tmp, buf, count)) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		ret = arch_nvram_ops.write(tmp, count, ppos);
+
+out:
+		kfree(tmp);
+		return ret;
+	}
 
-	spin_unlock_irq(&rtc_lock);
+	for (i = *ppos; count > 0 && i < nvram_size; ++i, ++p, --count) {
+		char c;
 
+		if (__get_user(c, p))
+			return -EFAULT;
+		arch_nvram_ops.write_byte(c, i);
+	}
 	*ppos = i;
-
-	return tmp - contents;
-
-checksum_err:
-	spin_unlock_irq(&rtc_lock);
-	return -EIO;
+	return p - buf;
 }
 
 static long nvram_misc_ioctl(struct file *file, unsigned int cmd,


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Thread

[RFC v4 00/25] Re-use nvram module Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 11/25] m68k/atari: Implement arch_nvram_ops methods and enable CONFIG_HAVE_ARCH_NVRAM_OPS Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 16/25] powerpc: Implement nvram sync ioctl Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 15/25] powerpc: Implement arch_nvram_ops.get_size() and remove old nvram_* exports Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 24/25] m68k/mac: Fix PRAM accessors Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 18/25] nvram: Drop nvram_* symbol exports and prototypes Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 14/25] powerpc: Add missing ppc_md.nvram_size for CHRP and PowerMac  Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 19/25] powerpc: Remove CONFIG_GENERIC_NVRAM and adopt CONFIG_HAVE_ARCH_NVRAM_OPS Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 09/25] char/nvram: Implement NVRAM read/write methods Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 13/25] powerpc: Cleanup nvram includes Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 10/25] char/nvram: Use generic fixed_size_llseek() Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 08/25] char/nvram: Allow the set_checksum and initialize ioctls to be omitted Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 01/25] scsi/atari_scsi: Dont select CONFIG_NVRAM Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 12/25] char/nvram: Add "devname:nvram" module alias Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 03/25] m68k/atari: Move Atari-specific code out of drivers/char/nvram.c Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
    Re: [RFC v4 03/25] m68k/atari: Move Atari-specific code out of  drivers/char/nvram.c Finn Thain <fthain@telegraphics.com.au> - 2015-07-14 10:20 +0200
      Re: [RFC v4 03/25] m68k/atari: Move Atari-specific code out of drivers/char/nvram.c Geert Uytterhoeven <geert@linux-m68k.org> - 2015-07-14 10:30 +0200
        Re: [RFC v4 03/25] m68k/atari: Move Atari-specific code out of drivers/char/nvram.c Andreas Schwab <schwab@linux-m68k.org> - 2015-07-14 10:40 +0200
  [RFC v4 21/25] powerpc: Adopt nvram module for PPC64 Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 25/25] m68k: Dispatch nvram_ops calls to Atari or Mac functions Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 23/25] m68k/mac: Use macros for RTC accesses not magic numbers Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 22/25] m68k/mac: Adopt naming and calling conventions for PRAM routines Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  [RFC v4 04/25] m68k/atari: Replace nvram_{read,write}_byte with arch_nvram_ops Finn Thain <fthain@telegraphics.com.au> - 2015-07-12 12:50 +0200
  Re: [RFC v4 00/25] Re-use nvram module Geert Uytterhoeven <geert@linux-m68k.org> - 2015-07-13 10:00 +0200

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