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diff --git a/doc/dev/rbd-export.rst b/doc/dev/rbd-export.rst new file mode 100644 index 000000000..2edb637f6 --- /dev/null +++ b/doc/dev/rbd-export.rst @@ -0,0 +1,104 @@ +RBD Export & Import +=================== + +This is a file format of an RBD image or snapshot. It's a sparse format +for the full image. There are three recording sections in the file. + +(1) Header. +(2) Metadata. +(3) Diffs. + +Header +~~~~~~ + +"rbd image v2\\n" + +Metadata records +~~~~~~~~~~~~~~~~ + +Every record has a one byte "tag" that identifies the record type, +followed by length of data, and then some other data. + +Metadata records come in the first part of the image. Order is not +important, as long as all the metadata records come before the data +records. + +In v2, we have the following metadata in each section: +(1 Bytes) tag. +(8 Bytes) length. +(n Bytes) data. + +In this way, we can skip the unrecognized tag. + +Image order +----------- + +- u8: 'O' +- le64: length of appending data (8) +- le64: image order + +Image format +------------ + +- u8: 'F' +- le64: length of appending data (8) +- le64: image format + +Image Features +-------------- + +- u8: 'T' +- le64: length of appending data (8) +- le64: image features + +Image Stripe unit +----------------- + +- u8: 'U' +- le64: length of appending data (8) +- le64: image striping unit + +Image Stripe count +------------------ + +- u8: 'C' +- le64: length of appending data (8) +- le64: image striping count + +ImageMeta Key and Value +----------------------- + +- u8: 'M' +- le64: length of appending data (length of key + length of value + 4 * 2) +- string: image-meta key +- string: image-meta value + +Final Record +~~~~~~~~~~~~ + +End +--- + +- u8: 'E' + + +Diffs records +~~~~~~~~~~~~~ + +Record the all snapshots and the HEAD in this section. + +Snap Protection status +---------------------- + +Record the snapshot's protection status if `--export-format=2`. +- u8: 'p' +- le64: length of appending data (8) +- u8: snap protection status (0 for false, 1 for true) + +Others +------ + +- le64: number of diffs +- Diffs ... + +Detail please refer to rbd-diff.rst |