英文:
C - copy local file using sendfile, should I check sent bytes?
问题
我在Linux上使用sendfile复制文件。下面是我使用它的示例
struct stat statBuf;
fstat(fdFrom, &statBuf);
sendfile(fd, fdFrom, 0, statBuf.st_size);
close(fd);
close(fdFrom);
sendfile的文档说它可能不会一次写入所有字节。我使用的方式安全吗？或者我应该实现一个循环，在循环中检查sendfile的结果直到为0？
描述符来自本地文件。
在从源文件复制字节之前，目标文件应该被截断为零吗？
英文:
I copy file on linux with sendfile. Below is the example how I use it
struct stat statBuf;
fstat(fdFrom, &statBuf);
sendfile(fd, fdFrom, 0, statBuf.st_size);
close(fd);
close(fdFrom);
Documentation to sendfile says that it may not write all bytes at once. Is the way how I use it safe? Or I should implement loop in which I check result of sendfile until will be 0?
Descriptors are from local files.
Should be target file truncated to zero before copying bytes from source file?
答案1
得分: 4
Yes, you should loop and sum up the bytes transferred until you've sent all of them. It could look something like this:
ssize_t rv;
for (off_t tot = 0; tot != statBuf.st_size; tot += (off_t)rv) {
rv = sendfile(fd, fdFrom, NULL, statBuf.st_size - tot);
if (rv == -1) {
// handle error
}
}
If you want the target file to be an exact copy, then yes, open it with the O_TRUNC flag set - or call ftruncate(fd, statBuf.st_size); after the copying has been done just in case the previous content was larger than what you just copied.
英文:
Yes, you should loop and sum up the bytes transfered until you've sent all of them. It could look something like this:
ssize_t rv;
for(off_t tot = 0; tot != statBuf.st_size; tot += (off_t)rv) {
rv = sendfile(fd, fdFrom, NULL, statBuf.st_size - tot);
if(rv == -1) {
// handle error
}
}
> Should be target file truncated to zero before copying bytes from source file?
If you want the target file to be an exact copy, then yes, open it with the O_TRUNC flag set - or call ftruncate(fd, statBuf.st_size); after the copying has been done just in case the previous content was larger than what you just copied.
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