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Subject[PATCH] support O_DIRECT in tmpfs/ramfs
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Hi,

A while ago there was a discussion about supporting direct-io on tmpfs.

Here is a simple patch that does it.

1. A new fs flag FS_RAM_BASED is added and the O_DIRECT flag is ignored
if this flag is set (suggestions on a better name?)

2. Specify FS_RAM_BASED for tmpfs and ramfs.

3. When EINVAL is returned only a fput is done. I changed it to go
through cleanup_all. But there is still a cleanup problem:

If a new file is created and then EINVAL is returned due to O_DIRECT,
the file is still left on the disk. I am not exactly sure how to fix
it other than adding another fs flag so we could check O_DIRECT
support at a much earlier stage. Comments on how to fix it?

Signed-off-by: Hua Zhong <hzhong@gmail.com>

diff --git a/fs/open.c b/fs/open.c
index c989fb4..c03285f 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -708,11 +708,13 @@ static struct file *__dentry_open(struct

/* NB: we're sure to have correct a_ops only after f_op->open */
if (f->f_flags & O_DIRECT) {
- if (!f->f_mapping->a_ops ||
- ((!f->f_mapping->a_ops->direct_IO) &&
- (!f->f_mapping->a_ops->get_xip_page))) {
- fput(f);
- f = ERR_PTR(-EINVAL);
+ if (dentry->d_sb->s_type->fs_flags & FS_RAM_BASED)
+ f->f_flags &= ~O_DIRECT;
+ else if (!f->f_mapping->a_ops ||
+ ((!f->f_mapping->a_ops->direct_IO) &&
+ (!f->f_mapping->a_ops->get_xip_page))) {
+ error = -EINVAL;
+ goto cleanup_all;
}
}

diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c
index 2faf4cd..0d4bebc 100644
--- a/fs/ramfs/inode.c
+++ b/fs/ramfs/inode.c
@@ -199,11 +199,13 @@ static int rootfs_get_sb(struct file_sys

static struct file_system_type ramfs_fs_type = {
.name = "ramfs",
+ .fs_flags = FS_RAM_BASED,
.get_sb = ramfs_get_sb,
.kill_sb = kill_litter_super,
};
static struct file_system_type rootfs_fs_type = {
.name = "rootfs",
+ .fs_flags = FS_RAM_BASED,
.get_sb = rootfs_get_sb,
.kill_sb = kill_litter_super,
};
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 186da81..0d95988 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -91,6 +91,7 @@ extern int dir_notify_enable;
/* public flags for file_system_type */
#define FS_REQUIRES_DEV 1
#define FS_BINARY_MOUNTDATA 2
+#define FS_RAM_BASED 8192 /* Ignore O_DIRECT */
#define FS_REVAL_DOT 16384 /* Check the paths ".", ".." for staleness */
#define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move()
* during rename() internally.
diff --git a/mm/shmem.c b/mm/shmem.c
index 70da7a0..5d23e8a 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2413,6 +2413,7 @@ static int shmem_get_sb(struct file_syst
static struct file_system_type tmpfs_fs_type = {
.owner = THIS_MODULE,
.name = "tmpfs",
+ .fs_flags = FS_RAM_BASED,
.get_sb = shmem_get_sb,
.kill_sb = kill_litter_super,
};
-
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