On 2019-10-21, Darrick J. Wong wrote: > On Tue, Oct 15, 2019 at 11:42:40AM -0700, Omar Sandoval wrote: > > From: Omar Sandoval > > > > 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 > > --- > > 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; > > Can we add some must-be-zero padding space at the end here for whomever > comes along next wanting to add more encoding info? I would suggest to copy the extension design of copy_struct_from_user(). Adding must-be-zero padding is a less-ideal solution to the extension problem than length-based extension. Also (I might be wrong) but shouldn't the __u64s be __aligned_u64 (as with syscall structure arguments)? > (And maybe a manpage and some basic testing, to reiterate Dave...) > > --D > > > +}; > > + > > /* 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 > > -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH