The golang http client does not return an error when a HTTP2 reply
includes a non-zero content length but does not return any data at all.
This scenario can occur e.g. when using rclone when a file stored in a
backend seems to be accessible but then fails to download.
If a pack file is missing try to determine the contained pack ids based
on the repository index. This helps with assessing the damage to a
repository before running `rebuild-index`.
Just passing the list of blobs to packsToBlobs would also work in most
cases, however, it could cause unexpected results when multiple pack
files have the same prefix. Forget found prefixes to prevent this.
Failed pack/blob downloads should be retried. For blobs that fail
decryption assume that the pack file is really damaged and try to
restore the remaining blobs.
* Stop prepending the operation name: it's already part of os.PathError,
leading to repetitive errors like "Chmod: chmod /foo/bar: operation not
permitted".
* Use errors.Is to check for specific errors.
Apparently readahead was disabled by default. Enable readahead with the
Linux default size of 128kB. Larger values seem to have no effect.
This can speed up reading from the fuse mount by at least factor 5.
Speedup for a 1G random file stored in a local repository:
(Only one result shown, but times were quite stable, restarted restic
after each command)
$ dd if=/dev/urandom bs=1M count=1024 of=rand
$ shasum -a 256 tmp/rand
75dd9b374e712577d64672a05b8ceee40dfc45dce6321082d2c2fd51d60c6c2d tmp/rand
before: $ time shasum -a 256 fuse/snapshots/latest/tmp/rand
75dd9b374e712577d64672a05b8ceee40dfc45dce6321082d2c2fd51d60c6c2d fuse/snapshots/latest/tmp/rand
real 0m18.294s
user 0m4.522s
sys 0m3.305s
before: $ time cat fuse/snapshots/latest/tmp/rand > /dev/null
real 0m14.924s
user 0m0.000s
sys 0m4.625s
after: $ time shasum -a 256 fuse/snapshots/latest/tmp/rand
75dd9b374e712577d64672a05b8ceee40dfc45dce6321082d2c2fd51d60c6c2d fuse/snapshots/latest/tmp/rand
real 0m6.106s
user 0m3.115s
sys 0m0.182s
after: $ time cat fuse/snapshots/latest/tmp/rand > /dev/null
real 0m3.096s
user 0m0.017s
sys 0m0.241s
Since the fileInfos are returned in a []interface, they're already
allocated on the heap. Making them pointers explicitly means the
compiler doesn't need to generate fileInfo and *fileInfo versions of the
methods on this type. The binary becomes about 7KiB smaller on
Linux/amd64.
