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Message-ID: <4F9AC770.8080004@redhat.com>
Date: Fri, 27 Apr 2012 11:21:04 -0500
From: Eric Sandeen <sandeen@...hat.com>
To: "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
CC: ext4 development <linux-ext4@...r.kernel.org>,
Andreas Dilger <adilger@...ger.ca>,
Bernd Schubert <bernd.schubert@...m.fraunhofer.de>
Subject: [PATCH] vfs: allow custom EOF in generic_file_llseek code
For ext3/4 htree directories, using the vfs llseek function with
SEEK_END goes to i_size like for any other file, but in reality
we want the maximum possible hash value. Recent changes
in ext4 have cut & pasted generic_file_llseek() back into fs/ext4/dir.c,
but replicating this core code seems like a bad idea, especially
since the copy has already diverged from the vfs.
This patch implements a version of generic_file_llseek which can accept
both a custom maximum offset, and a custom EOF position. With this
in place, ext4_dir_llseek can pass in the appropriate maximum hash
position for both maxsize and eof, and get what it wants.
As far as I know, this does not fix any bugs - nfs in the kernel
doesn't use SEEK_END, and I don't know of any user who does. But
some ext4 folks seem keen on doing the right thing here, and I can't
really argue.
(Patch also fixes up some comments slightly)
Signed-off-by: Eric Sandeen <sandeen@...hat.com>
---
diff --git a/fs/read_write.c b/fs/read_write.c
index ffc99d2..ecd1828 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -51,14 +51,15 @@ static loff_t lseek_execute(struct file *file, struct inode *inode,
}
/**
- * generic_file_llseek_size - generic llseek implementation for regular files
+ * generic_file_llseek_size_eof - generic llseek implementation for regular files
* @file: file structure to seek on
* @offset: file offset to seek to
* @origin: type of seek
- * @size: max size of file system
+ * @size: max size of this file in file system
+ * @eof: offset used for SEEK_END position
*
* This is a variant of generic_file_llseek that allows passing in a custom
- * file size.
+ * maximum file size and a custom EOF position, for e.g. hashed directories
*
* Synchronization:
* SEEK_SET and SEEK_END are unsynchronized (but atomic on 64bit platforms)
@@ -66,14 +67,14 @@ static loff_t lseek_execute(struct file *file, struct inode *inode,
* read/writes behave like SEEK_SET against seeks.
*/
loff_t
-generic_file_llseek_size(struct file *file, loff_t offset, int origin,
- loff_t maxsize)
+generic_file_llseek_size_eof(struct file *file, loff_t offset, int origin,
+ loff_t maxsize, loff_t eof)
{
struct inode *inode = file->f_mapping->host;
switch (origin) {
case SEEK_END:
- offset += i_size_read(inode);
+ offset += eof;
break;
case SEEK_CUR:
/*
@@ -99,7 +100,7 @@ generic_file_llseek_size(struct file *file, loff_t offset, int origin,
* In the generic case the entire file is data, so as long as
* offset isn't at the end of the file then the offset is data.
*/
- if (offset >= i_size_read(inode))
+ if (offset >= eof)
return -ENXIO;
break;
case SEEK_HOLE:
@@ -107,14 +108,35 @@ generic_file_llseek_size(struct file *file, loff_t offset, int origin,
* There is a virtual hole at the end of the file, so as long as
* offset isn't i_size or larger, return i_size.
*/
- if (offset >= i_size_read(inode))
+ if (offset >= eof)
return -ENXIO;
- offset = i_size_read(inode);
+ offset = eof;
break;
}
return lseek_execute(file, inode, offset, maxsize);
}
+EXPORT_SYMBOL(generic_file_llseek_size_eof);
+
+/**
+ * generic_file_llseek_size - generic llseek implementation for regular files
+ * @file: file structure to seek on
+ * @offset: file offset to seek to
+ * @origin: type of seek
+ * @size: max size of this file in file system
+ *
+ * This is a variant of generic_file_llseek that allows passing in a custom
+ * maximum file size.
+ */
+loff_t
+generic_file_llseek_size(struct file *file, loff_t offset, int origin,
+ loff_t maxsize)
+{
+ struct inode *inode = file->f_mapping->host;
+
+ return generic_file_llseek_size_eof(file, offset, origin, maxsize,
+ i_size_read(inode));
+}
EXPORT_SYMBOL(generic_file_llseek_size);
/**
@@ -131,8 +153,9 @@ loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
{
struct inode *inode = file->f_mapping->host;
- return generic_file_llseek_size(file, offset, origin,
- inode->i_sb->s_maxbytes);
+ return generic_file_llseek_size_eof(file, offset, origin,
+ inode->i_sb->s_maxbytes,
+ i_size_read(inode));
}
EXPORT_SYMBOL(generic_file_llseek);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8de6755..a6ae7a4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2402,6 +2402,8 @@ extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
extern loff_t generic_file_llseek_size(struct file *file, loff_t offset,
int origin, loff_t maxsize);
+extern loff_t generic_file_llseek_size_eof(struct file *file, loff_t offset,
+ int origin, loff_t maxsize, loff_t eof);
extern int generic_file_open(struct inode * inode, struct file * filp);
extern int nonseekable_open(struct inode * inode, struct file * filp);
--
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