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Add -o readonly option to FUSE driver

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This commit is contained in:
Marcus Holland-Moritz 2020-12-08 22:53:35 +01:00
parent 88dd18781b
commit 04c43ec421
4 changed files with 21 additions and 0 deletions
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10
doc/dwarfs.md
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@ -64,6 +64,16 @@ options:
will also consume more memory to hold the hardlink count table.
This will be 4 bytes for every regular file inode.
* `-o readonly`
Show all file system entries as read-only. By default, DwarFS
will preserve the original writeability, which is obviously a
lie as it's a read-only file system. However, this is needed
for overlays to work correctly, as otherwise directories are
seen as read-only by the overlay and it'll be impossible to
create new files even in a writeable overlay. If you don't use
overlays and want the file system to reflect its read-only
state, you can set this option.
* `-o (no_)cache_image`
By default, `dwarfs` tries to ensure that the compressed file
system image will not be cached by the kernel (i.e. the default

1
include/dwarfs/options.h
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@ -38,6 +38,7 @@ struct block_cache_options {
struct metadata_options {
bool enable_nlink{false};
bool readonly{false};
};
struct filesystem_options {

4
src/dwarfs.cpp
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@ -53,6 +53,7 @@ struct options {
const char* mlock_str; // TODO: const?? -> use string?
const char* decompress_ratio_str; // TODO: const?? -> use string?
int enable_nlink;
int readonly;
int cache_image;
int cache_files;
size_t cachesize;
@ -79,6 +80,7 @@ const struct fuse_opt dwarfs_opts[] = {
DWARFS_OPT("mlock=%s", mlock_str, 0),
DWARFS_OPT("decratio=%s", decompress_ratio_str, 0),
DWARFS_OPT("enable_nlink", enable_nlink, 1),
DWARFS_OPT("readonly", readonly, 1),
DWARFS_OPT("cache_image", cache_image, 1),
DWARFS_OPT("no_cache_image", cache_image, 0),
DWARFS_OPT("cache_files", cache_files, 1),
@ -105,6 +107,7 @@ void op_init(void* /*userdata*/, struct fuse_conn_info* /*conn*/) {
fsopts.block_cache.decompress_ratio = s_opts.decompress_ratio;
fsopts.block_cache.mm_release = !s_opts.cache_image;
fsopts.metadata.enable_nlink = bool(s_opts.enable_nlink);
fsopts.metadata.readonly = bool(s_opts.readonly);
s_fs = std::make_shared<filesystem_v2>(
s_lgr, std::make_shared<mmap>(s_opts.fsimage), fsopts,
&s_opts.stat_defaults, FUSE_ROOT_ID);
@ -400,6 +403,7 @@ void usage(const char* progname) {
<< " -o mlock=NAME mlock mode: (none), try, must\n"
<< " -o decratio=NUM ratio for full decompression (0.8)\n"
<< " -o enable_nlink show correct hardlink numbers\n"
<< " -o readonly show read-only file system\n"
<< " -o (no_)cache_image (don't) keep image in kernel cache\n"
<< " -o (no_)cache_files (don't) keep files in kernel cache\n"
<< " -o debuglevel=NAME error, warn, (info), debug, trace\n"

6
src/dwarfs/metadata_v2.cpp
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@ -95,6 +95,8 @@ void analyze_frozen(std::ostream& os,
os << '\n';
}
const uint16_t READ_ONLY_MASK = ~(S_IWUSR | S_IWGRP | S_IWOTH);
} // namespace
template <typename LoggerPolicy>
@ -637,6 +639,10 @@ int metadata_<LoggerPolicy>::getattr(entry_view entry,
stbuf->st_mode = mode;
if (options_.readonly) {
stbuf->st_mode &= READ_ONLY_MASK;
}
stbuf->st_size = S_ISDIR(mode) ? make_directory_view(entry).entry_count()
: file_size(entry, mode);
stbuf->st_ino = inode + inode_offset_;