Understanding the arguments to archive_read_disk_entry_from_file

[omgal...@gmail.com]

Hi all,

I have a fairly simple use case where I want to create an archive whose contents come from files in a disk. I saw that the man page for archive_read_disk_entry_from_file shows the following:

void
file_to_archive(struct archive *a, const char *name)
{
 char buff[8192];
 size_t bytes_read;
 struct archive *ard;
 struct archive_entry *entry;
 int fd;

 ard = archive_read_disk_new();
 archive_read_disk_set_standard_lookup(ard);
 entry = archive_entry_new();
 fd = open(name, O_RDONLY);
 if (fd < 0)
   return;
 archive_entry_copy_pathname(entry, name);
 archive_read_disk_entry_from_file(ard, entry, fd, NULL);
 archive_write_header(a, entry);
 while ((bytes_read = read(fd, buff, sizeof(buff))) > 0)
   archive_write_data(a, buff, bytes_read);
 archive_write_finish_entry(a);
 archive_read_free(ard);
 archive_entry_free(entry);
}

What's the purpose of the first struct archive* argument of archive_read_disk_entry_from_file? It doesn't seem to act like a handle for the disk file, since we're manually copying its path to the entry's pathname.

[Tim Kientzle]

`archive_read_disk_new()` creates an object that knows how to read information from the file system.

You can use it in two ways:

* You can attach it to a directory and use it to iterate over all the items in the directory. In essence, this treats a directory tree as an archive in it's own right. For example, bsdtar makes heavy use of this.

* In this situation, it's being used merely as a helper to look up information about the files on disk. Generally, you would create one of these objects and reuse it for many entries -- it builds up some internal caches of filesystem details that can help speed up certain operations.

Tim

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[Martin Galvan]

El sáb., 1 sept. 2018 a las 20:21, Tim Kientzle (<t...@kientzle.com>) escribió:
> * You can attach it to a directory and use it to iterate over all the items in the directory. In essence, this treats a directory tree as an archive in it's own right. For example, bsdtar makes heavy use of this.

Thanks for the answer. If I understood correctly, here the first
struct archive* acts as a sort of handle for a directory, right?