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@@ -464,29 +464,38 b' impl Repo {' | |||
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464 | 464 | let data_filename = format!("dirstate.{}", uuid); |
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465 | 465 | let data_filename = self.hg_vfs().join(data_filename); |
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466 | 466 | let mut options = std::fs::OpenOptions::new(); |
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467 | if append { | |
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468 | options.append(true); | |
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469 | } else { | |
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470 | options.write(true).create_new(true); | |
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467 | options.write(true); | |
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468 | ||
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469 | // Why are we not using the O_APPEND flag when appending? | |
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470 | // | |
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471 | // - O_APPEND makes it trickier to deal with garbage at the end of | |
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472 | // the file, left by a previous uncommitted transaction. By | |
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473 | // starting the write at [old_data_size] we make sure we erase | |
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474 | // all such garbage. | |
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475 | // | |
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476 | // - O_APPEND requires to special-case 0-byte writes, whereas we | |
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477 | // don't need that. | |
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478 | // | |
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479 | // - Some OSes have bugs in implementation O_APPEND: | |
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480 | // revlog.py talks about a Solaris bug, but we also saw some ZFS | |
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481 | // bug: https://github.com/openzfs/zfs/pull/3124, | |
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482 | // https://github.com/openzfs/zfs/issues/13370 | |
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483 | // | |
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484 | if !append { | |
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485 | options.create_new(true); | |
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471 | 486 | } |
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487 | ||
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472 | 488 | let data_size = (|| { |
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473 | 489 | // TODO: loop and try another random ID if !append and this |
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474 | 490 | // returns `ErrorKind::AlreadyExists`? Collision chance of two |
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475 | 491 | // random IDs is one in 2**32 |
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476 | 492 | let mut file = options.open(&data_filename)?; |
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477 |
if |
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478 | // If we're not appending anything, the data size is the | |
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479 | // same as in the previous docket. It is *not* the file | |
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480 | // length, since it could have garbage at the end. | |
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481 | // We don't have to worry about it when we do have data | |
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482 | // to append since we rewrite the root node in this case. | |
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483 | Ok(old_data_size as u64) | |
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484 | } else { | |
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485 | file.write_all(&data)?; | |
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486 | file.flush()?; | |
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487 | // TODO: use https://doc.rust-lang.org/std/io/trait.Seek.html#method.stream_position when we require Rust 1.51+ | |
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488 | file.seek(SeekFrom::Current(0)) | |
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493 | if append { | |
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494 | file.seek(SeekFrom::Start(old_data_size as u64))?; | |
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489 | 495 | } |
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496 | file.write_all(&data)?; | |
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497 | file.flush()?; | |
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498 | file.seek(SeekFrom::Current(0)) | |
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490 | 499 | })() |
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491 | 500 | .when_writing_file(&data_filename)?; |
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492 | 501 |
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