From: Omar Sandoval <osandov@xxxxxx>
Btrfs can transparently compress data written by the user. However, we'd
like to add an interface to write pre-compressed data directly to the
filesystem. This adds support for so-called "encoded writes" via
pwritev2().
A new RWF_ENCODED flags indicates that a write is "encoded". If this
flag is set, iov[0].iov_base points to a struct encoded_iov which
contains metadata about the write: namely, the compression algorithm and
the unencoded (i.e., decompressed) length of the extent. iov[0].iov_len
must be set to sizeof(struct encoded_iov), which can be used to extend
the interface in the future. The remaining iovecs contain the encoded
extent.
A similar interface for reading encoded data can be added to preadv2()
in the future.
Filesystems must indicate that they support encoded writes by setting
FMODE_ENCODED_IO in ->file_open().
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
---
include/linux/fs.h | 13 +++++++
include/uapi/linux/fs.h | 24 ++++++++++++-
mm/filemap.c | 75 ++++++++++++++++++++++++++++++++++-------
3 files changed, 99 insertions(+), 13 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 75c4b7680385..ae3ac0312674 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -175,6 +175,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/* File does not contribute to nr_files count */
#define FMODE_NOACCOUNT ((__force fmode_t)0x20000000)
+/* File supports encoded IO */
+#define FMODE_ENCODED_IO ((__force fmode_t)0x40000000)
+
/*
* Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
* that indicates that they should check the contents of the iovec are
@@ -314,6 +317,7 @@ enum rw_hint {
#define IOCB_SYNC (1 << 5)
#define IOCB_WRITE (1 << 6)
#define IOCB_NOWAIT (1 << 7)
+#define IOCB_ENCODED (1 << 8)
struct kiocb {
struct file *ki_filp;
@@ -3046,6 +3050,10 @@ extern int sb_min_blocksize(struct super_block *, int);
extern int generic_file_mmap(struct file *, struct vm_area_struct *);
extern int generic_file_readonly_mmap(struct file *, struct vm_area_struct *);
extern ssize_t generic_write_checks(struct kiocb *, struct iov_iter *);
+struct encoded_iov;
+extern int generic_encoded_write_checks(struct kiocb *, struct encoded_iov *);
+extern int import_encoded_write(struct kiocb *, struct encoded_iov *,
+ struct iov_iter *);
extern int generic_remap_checks(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
loff_t *count, unsigned int remap_flags);
@@ -3364,6 +3372,11 @@ static inline int kiocb_set_rw_flags(int rw, struct kiocb *ki, rwf_t flags)
return -EOPNOTSUPP;
ki->ki_flags |= IOCB_NOWAIT;
}
+ if (flags & RWF_ENCODED) {
+ if (rw != WRITE || !(ki->ki_filp->f_mode & FMODE_ENCODED_IO))
+ return -EOPNOTSUPP;
+ ki->ki_flags |= IOCB_ENCODED;
+ }
if (flags & RWF_HIPRI)
ki->ki_flags |= IOCB_HIPRI;
if (flags & RWF_DSYNC)
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index aad225b05be7..b775d9aea978 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -283,6 +283,25 @@ struct fsxattr {
typedef int __bitwise __kernel_rwf_t;
+enum {
+ ENCODED_IOV_COMPRESSION_NONE,
+ ENCODED_IOV_COMPRESSION_ZLIB,
+ ENCODED_IOV_COMPRESSION_LZO,
+ ENCODED_IOV_COMPRESSION_ZSTD,
+ ENCODED_IOV_COMPRESSION_TYPES = ENCODED_IOV_COMPRESSION_ZSTD,
+};
+
+enum {
+ ENCODED_IOV_ENCRYPTION_NONE,
+ ENCODED_IOV_ENCRYPTION_TYPES = ENCODED_IOV_ENCRYPTION_NONE,
+};
+
+struct encoded_iov {
+ __u64 unencoded_len;
+ __u32 compression;
+ __u32 encryption;
+};
+
/* high priority request, poll if possible */
#define RWF_HIPRI ((__force __kernel_rwf_t)0x00000001)
@@ -298,8 +317,11 @@ typedef int __bitwise __kernel_rwf_t;
/* per-IO O_APPEND */
#define RWF_APPEND ((__force __kernel_rwf_t)0x00000010)
+/* encoded (e.g., compressed or encrypted) IO */
+#define RWF_ENCODED ((__force __kernel_rwf_t)0x00000020)
+
/* mask of flags supported by the kernel */
#define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
- RWF_APPEND)
+ RWF_APPEND | RWF_ENCODED)
#endif /* _UAPI_LINUX_FS_H */
diff --git a/mm/filemap.c b/mm/filemap.c
index 40667c2f3383..3d2555364432 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2974,24 +2974,16 @@ static int generic_write_check_limits(struct file *file, loff_t pos,
return 0;
}
-/*
- * Performs necessary checks before doing a write
- *
- * Can adjust writing position or amount of bytes to write.
- * Returns appropriate error code that caller should return or
- * zero in case that write should be allowed.
- */
-inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
+static int generic_write_checks_common(struct kiocb *iocb, loff_t *count)
{
struct file *file = iocb->ki_filp;
struct inode *inode = file->f_mapping->host;
- loff_t count;
int ret;
if (IS_SWAPFILE(inode))
return -ETXTBSY;
- if (!iov_iter_count(from))
+ if (!*count)
return 0;
/* FIXME: this is for backwards compatibility with 2.4 */
@@ -3001,8 +2993,21 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
return -EINVAL;
- count = iov_iter_count(from);
- ret = generic_write_check_limits(file, iocb->ki_pos, &count);
+ return generic_write_check_limits(iocb->ki_filp, iocb->ki_pos, count);
+}
+
+/*
+ * Performs necessary checks before doing a write
+ *
+ * Can adjust writing position or amount of bytes to write.
+ * Returns a negative errno or the new number of bytes to write.
+ */
+inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
+{
+ loff_t count = iov_iter_count(from);
+ int ret;
+
+ ret = generic_write_checks_common(iocb, &count);
if (ret)
return ret;
@@ -3011,6 +3016,52 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
}
EXPORT_SYMBOL(generic_write_checks);
+int generic_encoded_write_checks(struct kiocb *iocb,
+ struct encoded_iov *encoded)
+{
+ loff_t count = encoded->unencoded_len;
+ int ret;
+
+ ret = generic_write_checks_common(iocb, &count);
+ if (ret)
+ return ret;
+
+ if (count != encoded->unencoded_len) {
+ /*
+ * The write got truncated by generic_write_checks(). We can't
+ * do a partial encoded write.
+ */
+ return -EFBIG;
+ }
+ return 0;
+}
+EXPORT_SYMBOL(generic_encoded_write_checks);
+
+/*
+ * If no encoding is set, this clears IOCB_ENCODED and the write should be
+ * treated as a normal write.
+ */
+int import_encoded_write(struct kiocb *iocb, struct encoded_iov *encoded,
+ struct iov_iter *from)
+{
+ if (iov_iter_single_seg_count(from) != sizeof(*encoded))
+ return -EINVAL;
+ if (copy_from_iter(encoded, sizeof(*encoded), from) != sizeof(*encoded))
+ return -EFAULT;
+ if (encoded->compression == ENCODED_IOV_COMPRESSION_NONE &&
+ encoded->encryption == ENCODED_IOV_ENCRYPTION_NONE) {
+ iocb->ki_flags &= ~IOCB_ENCODED;
+ return 0;
+ }
+ if (encoded->compression > ENCODED_IOV_COMPRESSION_TYPES ||
+ encoded->encryption > ENCODED_IOV_ENCRYPTION_TYPES)
+ return -EINVAL;
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+ return 0;
+}
+EXPORT_SYMBOL(import_encoded_write);
+
/*
* Performs necessary checks before doing a clone.
*
--
2.23.0
