From: Omar Sandoval <osandov@xxxxxx>
Btrfs supports transparent compression: data written by the user can be
compressed when written to disk and decompressed when read back.
However, we'd like to add an interface to write pre-compressed data
directly to the filesystem, and the matching interface to read
compressed data without decompressing it. This adds support for
so-called "encoded I/O" via preadv2() and pwritev2().
A new RWF_ENCODED flags indicates that a read or write is "encoded". If
this flag is set, iov[0].iov_base points to a struct encoded_iov which
is used for metadata: namely, the compression algorithm, unencoded
(i.e., decompressed) length, and what subrange of the unencoded data
should be used (needed for truncated or hole-punched extents and when
reading in the middle of an extent). For reads, the filesystem returns
this information; for writes, the caller provides it to the filesystem.
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.
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 | 14 +++++++
include/uapi/linux/fs.h | 26 ++++++++++++-
mm/filemap.c | 82 ++++++++++++++++++++++++++++++++++-------
3 files changed, 108 insertions(+), 14 deletions(-)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e0d909d35763..54681f21e05e 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;
@@ -3088,6 +3092,11 @@ 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 ssize_t check_encoded_read(struct kiocb *, struct iov_iter *);
+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);
@@ -3403,6 +3412,11 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
return -EOPNOTSUPP;
ki->ki_flags |= IOCB_NOWAIT;
}
+ if (flags & RWF_ENCODED) {
+ if (!(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 379a612f8f1d..ed92a8a257cb 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -284,6 +284,27 @@ 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 len;
+ __u64 unencoded_len;
+ __u64 unencoded_offset;
+ __u32 compression;
+ __u32 encryption;
+};
+
/* high priority request, poll if possible */
#define RWF_HIPRI ((__force __kernel_rwf_t)0x00000001)
@@ -299,8 +320,11 @@ 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 1146fcfa3215..d2e6d9caf353 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2948,24 +2948,15 @@ 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 */
@@ -2975,8 +2966,21 @@ 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;
@@ -2985,6 +2989,58 @@ 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_common(). We
+ * can't do a partial encoded write.
+ */
+ return -EFBIG;
+ }
+ return 0;
+}
+EXPORT_SYMBOL(generic_encoded_write_checks);
+
+ssize_t check_encoded_read(struct kiocb *iocb, struct iov_iter *iter)
+{
+ if (!(iocb->ki_filp->f_flags & O_ENCODED))
+ return -EPERM;
+ if (iov_iter_single_seg_count(iter) != sizeof(struct encoded_iov))
+ return -EINVAL;
+ return iov_iter_count(iter) - sizeof(struct encoded_iov);
+}
+EXPORT_SYMBOL(check_encoded_read);
+
+int import_encoded_write(struct kiocb *iocb, struct encoded_iov *encoded,
+ struct iov_iter *from)
+{
+ if (!(iocb->ki_filp->f_flags & O_ENCODED))
+ return -EPERM;
+ 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)
+ return -EINVAL;
+ if (encoded->compression > ENCODED_IOV_COMPRESSION_TYPES ||
+ encoded->encryption > ENCODED_IOV_ENCRYPTION_TYPES)
+ return -EINVAL;
+ if (encoded->unencoded_offset >= encoded->unencoded_len)
+ return -EINVAL;
+ return 0;
+}
+EXPORT_SYMBOL(import_encoded_write);
+
/*
* Performs necessary checks before doing a clone.
*
--
2.23.0
