Hi All, I just released a toy program, "fienode" which computes a SHA1 of the physical extents of a file.
Link: https://github.com/pwaller/fienode There are some questions around on the internet of how to find CoW copies, which I've answered: http://unix.stackexchange.com/questions/263309/how-to-verify-a-file-copy-is-reflink-cow/277043#277043 I would appreciate if anyone fact-checks me or has a better way :) Regards, - Peter P.S. A BRFS mystery: I did a cp --reflink of a large file, and within a few minutes, the extents of the copy changed, even though I did not intentionally change the file. But only the extents in the copy changed, not the original. filefrag -v file ext: logical_offset: physical_offset: length: expected: flags: 0: 0.. 32767: 516366448.. 516399215: 32768: 1: 32768.. 65535: 516430848.. 516463615: 32768: 516399216: 2: 65536.. 98303: 516463616.. 516496383: 32768: 3: 98304.. 131071: 516496384.. 516529151: 32768: 4: 131072.. 163839: 516529152.. 516561919: 32768: 5: 163840.. 180671: 516561920.. 516578751: 16832: 6: 180672.. 213439: 516579186.. 516611953: 32768: 516578752: 7: 213440.. 246207: 516611954.. 516644721: 32768: 8: 246208.. 278975: 516644722.. 516677489: 32768: 9: 278976.. 306431: 516399217.. 516426672: 27456: 516677490: 10: 306432.. 339199: 516692992.. 516725759: 32768: 516426673: 11: 339200.. 371967: 516725760.. 516758527: 32768: 12: 371968.. 404735: 516758528.. 516791295: 32768: 13: 404736.. 410059: 516791296.. 516796619: 5324: eof [ 5 minutes pass ] File size of x is 1679605760 (410060 blocks of 4096 bytes) ext: logical_offset: physical_offset: length: expected: flags: 0: 0.. 32767: 516366448.. 516399215: 32768: 1: 32768.. 98303: 516430848.. 516496383: 65536: 516399216: 2: 98304.. 131071: 516496384.. 516529151: 32768: 3: 131072.. 163839: 516529152.. 516561919: 32768: 4: 163840.. 180671: 516561920.. 516578751: 16832: 5: 180672.. 213439: 516579186.. 516611953: 32768: 516578752: 6: 213440.. 246207: 516611954.. 516644721: 32768: 7: 246208.. 278975: 516644722.. 516677489: 32768: 8: 278976.. 306431: 516399217.. 516426672: 27456: 516677490: 9: 306432.. 339199: 516692992.. 516725759: 32768: 516426673: 10: 339200.. 371967: 516725760.. 516758527: 32768: 11: 371968.. 404735: 516758528.. 516791295: 32768: 12: 404736.. 410059: 516791296.. 516796619: 5324: eof [ an hour passes ] File size of x is 1679605760 (410060 blocks of 4096 bytes) ext: logical_offset: physical_offset: length: expected: flags: 0: 0.. 32767: 516366448.. 516399215: 32768: 1: 32768.. 163839: 516430848.. 516561919: 131072: 516399216: 2: 163840.. 180671: 516561920.. 516578751: 16832: 3: 180672.. 213439: 516579186.. 516611953: 32768: 516578752: 4: 213440.. 246207: 516611954.. 516644721: 32768: 5: 246208.. 278975: 516644722.. 516677489: 32768: 6: 278976.. 306431: 516399217.. 516426672: 27456: 516677490: 7: 306432.. 339199: 516692992.. 516725759: 32768: 516426673: 8: 339200.. 371967: 516725760.. 516758527: 32768: 9: 371968.. 404735: 516758528.. 516791295: 32768: 10: 404736.. 410059: 516791296.. 516796619: 5324: eof Over time, some extents are being merged in the reflink copies. What mechanism is causing this, and why did it only happen to one of the CoW copies and not the other? -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
