Hi! On 2023/4/10 01:16, наб wrote:
Modelled after tmpfs(5) ‒ there's a listing of mount options, and a summary of limitations. The feature flags are described in mkfs.erofs, and they're versioned and maintained upstream quite well there, so no need to duplicate those, since you only care on image creation. The real value add is the mount options, but I cannot figure out how device_id and fsid interact with the system at large, so I just noted they're there.
Thanks for the document. Currently EROFS has two main userspace progs --- erofs-utils and Nydus [1]. Later maybe more userspace progs such as composefs[3]. device_id and fsid are mainly used for Nydus image service to keep its multiple layers, so that the data source of each chunk could be from such external blobs. erofs-utils (with the upcoming tarerofs) is having such use case as well, in that case, one image could consist of a manifest and several original tar blobs with different device_ids. So that you could directly mount a EROFS merged image with several tarballs. Note that erofs-utils support is still under development, you could refer to [2] [1] https://github.com/dragonflyoss/image-service https://github.com/dragonflyoss/image-service/blob/master/rafs/src/metadata/layout/v6.rs [2] https://lore.kernel.org/r/20230401072705.99060-1-hsiangkao@xxxxxxxxxxxxxxxxx [3] https://github.com/containers/composefs/pull/112
State as of 6.3-rc5. Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx> --- man5/erofs.5 | 84 ++++++++++++++++++++++++++++++++++++++++++++++ man5/filesystems.5 | 6 ++++ 2 files changed, 90 insertions(+) create mode 100644 man5/erofs.5 diff --git a/man5/erofs.5 b/man5/erofs.5 new file mode 100644 index 000000000..de5b56121 --- /dev/null +++ b/man5/erofs.5 @@ -0,0 +1,84 @@ +.\" Copyright (c) 2016 by Michael Kerrisk <mtk.manpages@xxxxxxxxx> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH erofs 5 (date) "Linux man-pages (unreleased)" +.SH NAME +erofs \- the Enhanced Read-Only File System +.SH DESCRIPTION +.B erofs +is a create-once read-only filesystem, +with support for compression and a multi-device backing store. +.PP +There are two inode formats: +32-byte compact with 16-bit UID/GID, 32-bit file size, and no file times, +and 64-byte extended with 32-bit UID/GID, 64-bit file size, +and a modification time +.RI ( st_mtim ). +.\" See fs/erofs/super.c:shmem_parse_options for options it supports. +.SS Mount options +.TP +.BR user_xattr / nouser_xattr +Controls whether +.I user +extended attributes are exposed. +Defaults to yes +.TP +.BR acl / noacl +Controls whether POSIX +.BR acl (5)s +are exposed. +Defaults to yes. +.TP +.BR cache_strategy = disabled | readahead | readaround +Cache allocation for compressed files: +never, if reading from start of file, regardless of position. +Defaults to +.BR readaround . +.TP +.BR dax ", " dax = always | never +Direct Access control. +If +.B always +and the source device supports DAX, uncompressed non-inlined files +will be read directly, without going through the page cache. +.B dax +is a synonym for +.BR always . +Defaults to unset, which is equivalent to +.BR never . +.TP +.BR device = \fIblobdev\fP +Add extra device holding some of the data. +Must be given as many times and in the same order as +.B \-\-blobdev +was to +.BR mkfs.erofs (8). +.\" Nominally there's a device_table feature and it somehow scans(?) for them, +.\" cf. super.c:erofs_scan_devices(), but I haven't gotten it to work
See above.
+.TP +.BR domain_id = \fIdid\fP ", " fsid = \fIid\fP +Control CacheFiles on-demand read support. +To be documented.
See above and https://github.com/dragonflyoss/image-service/blob/master/docs/nydus-fscache.md Currently the main user is still Nydus since on-demand read quite relies on high-level stuffs (such as container registries, etc.). But we could develop a fscache API interfaces to erofs-utils later as well if some new users would like to use it with erofs-utils. Thanks, Gao Xiang
+.RE +.IP +.SH VERSIONS +.B erofs +images are versioed through the use of feature flags; +these are listed in the +.B \-E +section of +.BR mkfs.erofs (1), +.SH NOTES +The kernel must be configured with the +.B CONFIG_EROFS_FS +option to mount EROFS filesystems. +There are sub-configuration items that restrict the availability +of some of the parameters above. +.SH SEE ALSO +.BR mkfs.erofs (1), +.BR fsck.erofs (1), +.BR dump.erofs (1) +.PP +.I Documentation/filesystems/erofs.txt +in the kernel source. diff --git a/man5/filesystems.5 b/man5/filesystems.5 index 3c15f14da..c9b0bf695 100644 --- a/man5/filesystems.5 +++ b/man5/filesystems.5 @@ -48,6 +48,12 @@ filesystems in the Linux kernel. See the kernel documentation for a comprehensive description of all options and limitations. .TP 10 +.B erofs +is the Enhanced Read-Only File System, stable since Linux 5.4. +.\" commit 47e4937a4a7ca4184fd282791dfee76c6799966a moves it out of staging +See +.BR erofs (5). +.TP .B ext is an elaborate extension of the .B minix
