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basic/efivars: do not return EIO if an efivar read is shorten than fstat size
On my machine stat returns size 22, but only 20 bytes are read: openat(AT_FDCWD, "/sys/firmware/efi/efivars/LoaderTimeInitUSec-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f", O_RDONLY|O_NOCTTY|O_CLOEXEC) = 3 fstat(3, {st_mode=S_IFREG|0644, st_size=22, ...}) = 0 read(3, "\6\0\0\0", 4) = 4 read(3, "7\0001\0001\0003\0005\0002\0007\0\0\0", 18) = 16 Failed to read LoaderTimeInitUSec: Input/output error Let's just accept that the kernel is returning inconsistent results. It seems to happen two only two variables on my machine: /sys/firmware/efi/efivars/LoaderTimeInitUSec-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f /sys/firmware/efi/efivars/LoaderTimeMenuUSec-4a67b082-0a4c-41cf-b6c7-440b29bb8c4f so it might be related to the way we write them.
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@ -90,13 +90,14 @@ int efi_get_variable(
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n = read(fd, buf, (size_t) st.st_size - 4);
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if (n < 0)
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return -errno;
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if (n != st.st_size - 4)
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return -EIO;
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assert(n <= st.st_size - 4);
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/* Always NUL terminate (2 bytes, to protect UTF-16) */
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((char*) buf)[st.st_size - 4] = 0;
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((char*) buf)[st.st_size - 4 + 1] = 0;
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}
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((char*) buf)[n - 4] = 0;
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((char*) buf)[n - 4 + 1] = 0;
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} else
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/* Assume that the reported size is accurate */
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n = st.st_size - 4;
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/* Note that efivarfs interestingly doesn't require ftruncate() to update an existing EFI variable
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* with a smaller value. */
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@ -108,7 +109,7 @@ int efi_get_variable(
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*ret_value = TAKE_PTR(buf);
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if (ret_size)
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*ret_size = (size_t) st.st_size - 4;
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*ret_size = n;
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return 0;
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}
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