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ext4: support STATX_DIOALIGN 

Add support for STATX_DIOALIGN to ext4, so that direct I/O alignment
restrictions are exposed to userspace in a generic way.

Acked-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20220827065851.135710-5-ebiggers@kernel.org
This commit is contained in:
Eric Biggers 2022-08-26 23:58:47 -07:00
parent 53dd3f802a
commit 8434ef1d8a
3 changed files with 64 additions and 16 deletions
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1
fs/ext4/ext4.h
View File

@ -2979,6 +2979,7 @@ extern struct inode *__ext4_iget(struct super_block *sb, unsigned long ino,
extern int ext4_write_inode(struct inode *, struct writeback_control *);
extern int ext4_setattr(struct user_namespace *, struct dentry *,
struct iattr *);
extern u32 ext4_dio_alignment(struct inode *inode);
extern int ext4_getattr(struct user_namespace *, const struct path *,
struct kstat *, u32, unsigned int);
extern void ext4_evict_inode(struct inode *);

42
fs/ext4/file.c
View File

@ -36,24 +36,34 @@
#include "acl.h"
#include "truncate.h"
static bool ext4_dio_supported(struct kiocb *iocb, struct iov_iter *iter)
/*
* Returns %true if the given DIO request should be attempted with DIO, or
* %false if it should fall back to buffered I/O.
*
* DIO isn't well specified; when it's unsupported (either due to the request
* being misaligned, or due to the file not supporting DIO at all), filesystems
* either fall back to buffered I/O or return EINVAL. For files that don't use
* any special features like encryption or verity, ext4 has traditionally
* returned EINVAL for misaligned DIO. iomap_dio_rw() uses this convention too.
* In this case, we should attempt the DIO, *not* fall back to buffered I/O.
*
* In contrast, in cases where DIO is unsupported due to ext4 features, ext4
* traditionally falls back to buffered I/O.
*
* This function implements the traditional ext4 behavior in all these cases.
*/
static bool ext4_should_use_dio(struct kiocb *iocb, struct iov_iter *iter)
{
struct inode *inode = file_inode(iocb->ki_filp);
u32 dio_align = ext4_dio_alignment(inode);
if (IS_ENCRYPTED(inode)) {
if (!fscrypt_dio_supported(inode))
return false;
if (!IS_ALIGNED(iocb->ki_pos | iov_iter_alignment(iter),
i_blocksize(inode)))
return false;
}
if (fsverity_active(inode))
if (dio_align == 0)
return false;
if (ext4_should_journal_data(inode))
return false;
if (ext4_has_inline_data(inode))
return false;
return true;
if (dio_align == 1)
return true;
return IS_ALIGNED(iocb->ki_pos | iov_iter_alignment(iter), dio_align);
}
static ssize_t ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
@ -68,7 +78,7 @@ static ssize_t ext4_dio_read_iter(struct kiocb *iocb, struct iov_iter *to)
inode_lock_shared(inode);
}
if (!ext4_dio_supported(iocb, to)) {
if (!ext4_should_use_dio(iocb, to)) {
inode_unlock_shared(inode);
/*
* Fallback to buffered I/O if the operation being performed on
@ -516,7 +526,7 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
}
/* Fallback to buffered I/O if the inode does not support direct I/O. */
if (!ext4_dio_supported(iocb, from)) {
if (!ext4_should_use_dio(iocb, from)) {
if (ilock_shared)
inode_unlock_shared(inode);
else

37
fs/ext4/inode.c
View File

@ -5550,6 +5550,22 @@ err_out:
return error;
}
u32 ext4_dio_alignment(struct inode *inode)
{
if (fsverity_active(inode))
return 0;
if (ext4_should_journal_data(inode))
return 0;
if (ext4_has_inline_data(inode))
return 0;
if (IS_ENCRYPTED(inode)) {
if (!fscrypt_dio_supported(inode))
return 0;
return i_blocksize(inode);
}
return 1; /* use the iomap defaults */
}
int ext4_getattr(struct user_namespace *mnt_userns, const struct path *path,
struct kstat *stat, u32 request_mask, unsigned int query_flags)
{
@ -5565,6 +5581,27 @@ int ext4_getattr(struct user_namespace *mnt_userns, const struct path *path,
stat->btime.tv_nsec = ei->i_crtime.tv_nsec;
}
/*
* Return the DIO alignment restrictions if requested. We only return
* this information when requested, since on encrypted files it might
* take a fair bit of work to get if the file wasn't opened recently.
*/
if ((request_mask & STATX_DIOALIGN) && S_ISREG(inode->i_mode)) {
u32 dio_align = ext4_dio_alignment(inode);
stat->result_mask |= STATX_DIOALIGN;
if (dio_align == 1) {
struct block_device *bdev = inode->i_sb->s_bdev;
/* iomap defaults */
stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
stat->dio_offset_align = bdev_logical_block_size(bdev);
} else {
stat->dio_mem_align = dio_align;
stat->dio_offset_align = dio_align;
}
}
flags = ei->i_flags & EXT4_FL_USER_VISIBLE;
if (flags & EXT4_APPEND_FL)
stat->attributes |= STATX_ATTR_APPEND;