Handle large read/write/sendfile to File; return actual bytes written #60321
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The return value for the `jl_fs_write/read/sendfile` functions is an `int`, even through they all take `size_t` length arguments, resulting in potentially truncated counts for large file operations. Instead, on success (including partial read/write), we should return the `uv_fs_t.result` field. I have added a test for this but have left it disabled because it allocates a 5 GiB Vector to read into. One consequence of the truncated return values is that we previously mangled large files while copying them with sendfile. If the return value is truncated to a random negative value, it manifests as JuliaLang#30723 or JuliaLang#39868. If it is truncated to a positive value, sendfile will create a very large destination file with thousands of repeated sections of the source file, causing JuliaLang#56537. The bug will only manifest if LLVM decides to zero-extend the return value. This also changes `jl_fs_write` to return the actual number of bytes written, rather than the number of bytes it was asked to write. If a write returns EAGAIN (usually because the file is O_NONBLOCK/O_NODELAY), we never see the actual number of bytes written.
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Dec 9, 2025
| { | ||
| uv_fs_t req; | ||
| JL_SIGATOMIC_BEGIN(); | ||
| int ret = uv_fs_sendfile(unused_uv_loop_arg, &req, dst_fd, src_fd, |
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| int ret = uv_fs_sendfile(unused_uv_loop_arg, &req, dst_fd, src_fd, | |
| ssize_t ret = uv_fs_sendfile(unused_uv_loop_arg, &req, dst_fd, src_fd, |
and same below?
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I'm not sure I understand the suggestion. Does this avoid a bad implicit conversion later on?
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It's more for consistency: the function is supposed to return an ssize_t now, but the value returned is an int
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The return value for the
jl_fs_write/read/sendfilefunctions is anint, even through they all takesize_tlength arguments, resulting in potentially truncated counts for large file operations. Instead, on success (including partial read/write), we should return theuv_fs_t.resultfield.I have added a test for this but have left it disabled because it allocates a 5 GiB Vector to read into.
One consequence of the truncated return values is that we previously mangled large files while copying them with sendfile. If the return value is truncated to a random negative value, it manifests as #30723 or #39868. If it is truncated to a positive value, sendfile will create a very large destination file with thousands of repeated sections of the source file, causing #56537. The bug will only manifest if LLVM decides to zero-extend the return value.
This also changes
jl_fs_writeto return the actual number of bytes written, rather than the number of bytes it was asked to write. If a write returns EAGAIN (usually because the file is O_NONBLOCK/O_NODELAY), we never see the actual number of bytes written.