sys_fallocate() implementation on i386, x86_64 and powerpc

fallocate() is a new system call being proposed here which will allow
applications to preallocate space to any file(s) in a file system.
Each file system implementation that wants to use this feature will need
to support an inode operation called ->fallocate().
Applications can use this feature to avoid fragmentation to certain
level and thus get faster access speed. With preallocation, applications
also get a guarantee of space for particular file(s) - even if later the
the system becomes full.

Currently, glibc provides an interface called posix_fallocate() which
can be used for similar cause. Though this has the advantage of working
on all file systems, but it is quite slow (since it writes zeroes to
each block that has to be preallocated). Without a doubt, file systems
can do this more efficiently within the kernel, by implementing
the proposed fallocate() system call. It is expected that
posix_fallocate() will be modified to call this new system call first
and incase the kernel/filesystem does not implement it, it should fall
back to the current implementation of writing zeroes to the new blocks.
ToDos:
1. Implementation on other architectures (other than i386, x86_64,
   and ppc). Patches for s390(x) and ia64 are already available from
   previous posts, but it was decided that they should be added later
   once fallocate is in the mainline. Hence not including those patches
   in this take.
2. Changes to glibc,
   a) to support fallocate() system call
   b) to make posix_fallocate() and posix_fallocate64() call fallocate()

Signed-off-by: Amit Arora <aarora@in.ibm.com>

3 files changed, 9 insertions, 0 deletions

diff --git a/include/linux/falloc.h b/include/linux/falloc.h
new file mode 100644
index 000000000000..8e912ab6a072
--- /dev/null
+++ b/include/linux/falloc.h
@@ -0,0 +1,6 @@
+#ifndef _FALLOC_H_
+#define _FALLOC_H_
+
+#define FALLOC_FL_KEEP_SIZE	0x01 /* default is extend size */
+
+#endif /* _FALLOC_H_ */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 98205f680476..0b806c5e32eb 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1147,6 +1147,8 @@ struct inode_operations {
 	ssize_t (*listxattr) (struct dentry *, char *, size_t);
 	int (*removexattr) (struct dentry *, const char *);
 	void (*truncate_range)(struct inode *, loff_t, loff_t);
+	long (*fallocate)(struct inode *inode, int mode, loff_t offset,
+			  loff_t len);
 };
 
 struct seq_file;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 83d0ec11235e..7a8b1e3322e0 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -610,6 +610,7 @@ asmlinkage long sys_signalfd(int ufd, sigset_t __user *user_mask, size_t sizemas
 asmlinkage long sys_timerfd(int ufd, int clockid, int flags,
 			    const struct itimerspec __user *utmr);
 asmlinkage long sys_eventfd(unsigned int count);
+asmlinkage long sys_fallocate(int fd, int mode, loff_t offset, loff_t len);
 
 int kernel_execve(const char *filename, char *const argv[], char *const envp[]);