builder: align file dump order with prefetch list, fix #1488

[hangvane]

Relevant Issue (if applicable)

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Fix #1488

Details

Please describe the details of PullRequest.

1. The dump order for prefetch files does not match the order specified in prefetch list, so let's fix it, by recording the index of matched prefetch pattern, and then sort the prefetch files by indexes before dump.

Master:

Patch:

2. The construction of Prefetch is slow due to inefficient matching of prefetch patterns.
   For the build of patterns, generate_patterns(), the check whether current pattern is existed or covered by existing patterns in prefetch.patterns, is changed from iterating every pattern to check whether the parent path have been recorded.
   For the build of prefetch.files, the rootfs tree is iterated in BFS only once in build_rafs(), and then cached in Prefetch to aviod duplicate BFS iteration in layout_blob_simple().

3. Unit tests for prefetch are added.

Thus the build time prefetching is accelerated. For the nydusify convert time of a single layer Wordpress image with a total of 14,916 files, out of which 3,205 are prefetching files,

Master:
DirectoryToRafs: 19.13s
TarToRafs: 17.43s

Patch:
DirectoryToRafs: 7.08s
TarToRafs: 5.33s

Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

Go over all the following points, and put an x in all the boxes that apply.

• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Merging #1492 (2379ec4) into master (e2b131e) will increase coverage by 0.20%.
The diff coverage is 94.70%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1492      +/-   ##
==========================================
+ Coverage   62.50%   62.70%   +0.20%     
==========================================
  Files         123      123              
  Lines       43148    43248     +100     
  Branches    43148    43248     +100     
==========================================
+ Hits        26970    27119     +149     
+ Misses      14870    14818      -52     
- Partials     1308     1311       +3     

Files	Coverage Δ
builder/src/core/bootstrap.rs	77.33% <100.00%> (-0.16%)	⬇️
builder/src/stargz.rs	74.67% <100.00%> (ø)
builder/src/tarball.rs	62.84% <100.00%> (ø)
builder/src/core/blob.rs	41.33% <0.00%> (-0.07%)	⬇️
builder/src/core/layout.rs	92.10% <96.55%> (+92.10%)	⬆️
builder/src/directory.rs	0.00% <0.00%> (ø)
builder/src/core/prefetch.rs	74.70% <95.68%> (+28.41%)	⬆️

... and 1 file with indirect coverage changes

[jiangliu]

LGTM, thanks for the great work:)