* [PATCH-v2] erofs: code for verifying superblock checksum of an erofs image. @ 2019-10-22 15:39 Pratik Shinde 2019-10-22 16:34 ` Gao Xiang via Linux-erofs 0 siblings, 1 reply; 4+ messages in thread From: Pratik Shinde @ 2019-10-22 15:39 UTC (permalink / raw) To: linux-erofs, gaoxiang25, yuchao0; +Cc: linux-kernel Patch for kernel side changes of checksum feature.Used kernel's crc32c library for calculating the checksum. Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com> --- fs/erofs/erofs_fs.h | 5 +++-- fs/erofs/internal.h | 3 ++- fs/erofs/super.c | 33 +++++++++++++++++++++++++++++++++ 3 files changed, 38 insertions(+), 3 deletions(-) diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h index b1ee565..4d8097a 100644 --- a/fs/erofs/erofs_fs.h +++ b/fs/erofs/erofs_fs.h @@ -17,6 +17,7 @@ */ #define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING 0x00000001 #define EROFS_ALL_FEATURE_INCOMPAT EROFS_FEATURE_INCOMPAT_LZ4_0PADDING +#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001 /* 128-byte erofs on-disk super block */ struct erofs_super_block { @@ -37,8 +38,8 @@ struct erofs_super_block { __u8 uuid[16]; /* 128-bit uuid for volume */ __u8 volume_name[16]; /* volume name */ __le32 feature_incompat; - - __u8 reserved2[44]; + __le32 chksum_blocks; /* number of blocks used for checksum */ + __u8 reserved2[40]; }; /* diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h index 544a453..cec27ca 100644 --- a/fs/erofs/internal.h +++ b/fs/erofs/internal.h @@ -86,7 +86,7 @@ struct erofs_sb_info { u8 uuid[16]; /* 128-bit uuid for volume */ u8 volume_name[16]; /* volume name */ u32 feature_incompat; - + u32 feature_compat; unsigned int mount_opt; }; @@ -426,6 +426,7 @@ static inline void z_erofs_exit_zip_subsystem(void) {} #endif /* !CONFIG_EROFS_FS_ZIP */ #define EFSCORRUPTED EUCLEAN /* Filesystem is corrupted */ +#define EFSBADCRC EBADMSG /* Bad crc found */ #endif /* __EROFS_INTERNAL_H */ diff --git a/fs/erofs/super.c b/fs/erofs/super.c index 0e36949..9cda72d 100644 --- a/fs/erofs/super.c +++ b/fs/erofs/super.c @@ -9,6 +9,7 @@ #include <linux/statfs.h> #include <linux/parser.h> #include <linux/seq_file.h> +#include <linux/crc32c.h> #include "xattr.h" #define CREATE_TRACE_POINTS @@ -46,6 +47,31 @@ void _erofs_info(struct super_block *sb, const char *function, va_end(args); } +static int erofs_validate_sb_chksum(struct erofs_super_block *dsb, + struct super_block *sb) +{ + u32 disk_chksum, nblocks, crc = 0; + void *kaddr; + struct page *page; + int i; + + disk_chksum = le32_to_cpu(dsb->checksum); + nblocks = le32_to_cpu(dsb->chksum_blocks); + dsb->checksum = 0; + for (i = 0; i < nblocks; i++) { + page = erofs_get_meta_page(sb, i); + if (IS_ERR(page)) + return PTR_ERR(page); + kaddr = kmap(page); + crc = crc32c(crc, kaddr, EROFS_BLKSIZ); + kunmap(page); + unlock_page(page); + } + if (crc != disk_chksum) + return -EFSBADCRC; + return 0; +} + static void erofs_inode_init_once(void *ptr) { struct erofs_inode *vi = ptr; @@ -121,6 +147,13 @@ static int erofs_read_superblock(struct super_block *sb) goto out; } + if (dsb->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) { + ret = erofs_validate_sb_chksum(dsb, sb); + if (ret < 0) { + erofs_err(sb, "super block checksum incorrect"); + goto out; + } + } blkszbits = dsb->blkszbits; /* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */ if (blkszbits != LOG_BLOCK_SIZE) { -- 2.9.3 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH-v2] erofs: code for verifying superblock checksum of an erofs image. 2019-10-22 15:39 [PATCH-v2] erofs: code for verifying superblock checksum of an erofs image Pratik Shinde @ 2019-10-22 16:34 ` Gao Xiang via Linux-erofs 2019-10-22 16:48 ` Pratik Shinde 0 siblings, 1 reply; 4+ messages in thread From: Gao Xiang via Linux-erofs @ 2019-10-22 16:34 UTC (permalink / raw) To: Pratik Shinde; +Cc: linux-erofs, linux-kernel Hi Pratik, Some comments as below... On Tue, Oct 22, 2019 at 09:09:56PM +0530, Pratik Shinde wrote: > Patch for kernel side changes of checksum feature.Used kernel's > crc32c library for calculating the checksum. > > Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com> > --- > fs/erofs/erofs_fs.h | 5 +++-- > fs/erofs/internal.h | 3 ++- > fs/erofs/super.c | 33 +++++++++++++++++++++++++++++++++ > 3 files changed, 38 insertions(+), 3 deletions(-) > > diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h > index b1ee565..4d8097a 100644 > --- a/fs/erofs/erofs_fs.h > +++ b/fs/erofs/erofs_fs.h > @@ -17,6 +17,7 @@ > */ > #define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING 0x00000001 > #define EROFS_ALL_FEATURE_INCOMPAT EROFS_FEATURE_INCOMPAT_LZ4_0PADDING > +#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001 > > /* 128-byte erofs on-disk super block */ > struct erofs_super_block { > @@ -37,8 +38,8 @@ struct erofs_super_block { > __u8 uuid[16]; /* 128-bit uuid for volume */ > __u8 volume_name[16]; /* volume name */ > __le32 feature_incompat; > - > - __u8 reserved2[44]; > + __le32 chksum_blocks; /* number of blocks used for checksum */ > + __u8 reserved2[40]; > }; > > /* > diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h > index 544a453..cec27ca 100644 > --- a/fs/erofs/internal.h > +++ b/fs/erofs/internal.h > @@ -86,7 +86,7 @@ struct erofs_sb_info { > u8 uuid[16]; /* 128-bit uuid for volume */ > u8 volume_name[16]; /* volume name */ > u32 feature_incompat; > - > + u32 feature_compat; > unsigned int mount_opt; > }; > > @@ -426,6 +426,7 @@ static inline void z_erofs_exit_zip_subsystem(void) {} > #endif /* !CONFIG_EROFS_FS_ZIP */ > > #define EFSCORRUPTED EUCLEAN /* Filesystem is corrupted */ > +#define EFSBADCRC EBADMSG /* Bad crc found */ > > #endif /* __EROFS_INTERNAL_H */ > > diff --git a/fs/erofs/super.c b/fs/erofs/super.c > index 0e36949..9cda72d 100644 > --- a/fs/erofs/super.c > +++ b/fs/erofs/super.c > @@ -9,6 +9,7 @@ > #include <linux/statfs.h> > #include <linux/parser.h> > #include <linux/seq_file.h> > +#include <linux/crc32c.h> > #include "xattr.h" > > #define CREATE_TRACE_POINTS > @@ -46,6 +47,31 @@ void _erofs_info(struct super_block *sb, const char *function, > va_end(args); > } > > +static int erofs_validate_sb_chksum(struct erofs_super_block *dsb, > + struct super_block *sb) > +{ > + u32 disk_chksum, nblocks, crc = 0; > + void *kaddr; > + struct page *page; > + int i; > + > + disk_chksum = le32_to_cpu(dsb->checksum); > + nblocks = le32_to_cpu(dsb->chksum_blocks); We cannot write the page data directly since the page cache should be kept in sync with ondisk data (or for read-write fs, if it's claimed as uptodated, and it is modified later, you should mark it dirty, and do writeback then, but that is not the erofs case.) > + dsb->checksum = 0; > + for (i = 0; i < nblocks; i++) { > + page = erofs_get_meta_page(sb, i); > + if (IS_ERR(page)) > + return PTR_ERR(page); > + kaddr = kmap(page); Here kmap_atomic(page) is better. what I mean is kmap_atomic() in the caller erofs_read_superblock(), it should be replaced to kmap() instead. > + crc = crc32c(crc, kaddr, EROFS_BLKSIZ); > + kunmap(page); > + unlock_page(page); need put_page(page); I'm not sure whether I explained quite well, but this patch needs something to do. I'm now working on demonstrating new XZ algorithm and releasing erofs-utils v1.0. You can give more tries or I will help later. :-) Thanks, Gao Xiang > + } > + if (crc != disk_chksum) > + return -EFSBADCRC; > + return 0; > +} > + > static void erofs_inode_init_once(void *ptr) > { > struct erofs_inode *vi = ptr; > @@ -121,6 +147,13 @@ static int erofs_read_superblock(struct super_block *sb) > goto out; > } > > + if (dsb->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) { > + ret = erofs_validate_sb_chksum(dsb, sb); > + if (ret < 0) { > + erofs_err(sb, "super block checksum incorrect"); > + goto out; > + } > + } > blkszbits = dsb->blkszbits; > /* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */ > if (blkszbits != LOG_BLOCK_SIZE) { > -- > 2.9.3 > ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH-v2] erofs: code for verifying superblock checksum of an erofs image. 2019-10-22 16:34 ` Gao Xiang via Linux-erofs @ 2019-10-22 16:48 ` Pratik Shinde 2019-10-22 17:03 ` Gao Xiang via Linux-erofs 0 siblings, 1 reply; 4+ messages in thread From: Pratik Shinde @ 2019-10-22 16:48 UTC (permalink / raw) To: Gao Xiang; +Cc: linux-erofs, linux-kernel [-- Attachment #1: Type: text/plain, Size: 5218 bytes --] Hi Gao, Understood your concern. Can we do something like : 1) Allocate one buf of size EROFS_BLKSIZ 2) Read one page at a time into buf(memcpy) .call crc32c for it. In this way we won't be writing directly into page data and will not do large allocation. What do you think? --Pratik On Tue, 22 Oct, 2019, 10:04 PM Gao Xiang, <hsiangkao@aol.com> wrote: > Hi Pratik, > > Some comments as below... > > On Tue, Oct 22, 2019 at 09:09:56PM +0530, Pratik Shinde wrote: > > Patch for kernel side changes of checksum feature.Used kernel's > > crc32c library for calculating the checksum. > > > > Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com> > > --- > > fs/erofs/erofs_fs.h | 5 +++-- > > fs/erofs/internal.h | 3 ++- > > fs/erofs/super.c | 33 +++++++++++++++++++++++++++++++++ > > 3 files changed, 38 insertions(+), 3 deletions(-) > > > > diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h > > index b1ee565..4d8097a 100644 > > --- a/fs/erofs/erofs_fs.h > > +++ b/fs/erofs/erofs_fs.h > > @@ -17,6 +17,7 @@ > > */ > > #define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING 0x00000001 > > #define EROFS_ALL_FEATURE_INCOMPAT > EROFS_FEATURE_INCOMPAT_LZ4_0PADDING > > +#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001 > > > > /* 128-byte erofs on-disk super block */ > > struct erofs_super_block { > > @@ -37,8 +38,8 @@ struct erofs_super_block { > > __u8 uuid[16]; /* 128-bit uuid for volume */ > > __u8 volume_name[16]; /* volume name */ > > __le32 feature_incompat; > > - > > - __u8 reserved2[44]; > > + __le32 chksum_blocks; /* number of blocks used for checksum */ > > + __u8 reserved2[40]; > > }; > > > > /* > > diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h > > index 544a453..cec27ca 100644 > > --- a/fs/erofs/internal.h > > +++ b/fs/erofs/internal.h > > @@ -86,7 +86,7 @@ struct erofs_sb_info { > > u8 uuid[16]; /* 128-bit uuid for volume */ > > u8 volume_name[16]; /* volume name */ > > u32 feature_incompat; > > - > > + u32 feature_compat; > > unsigned int mount_opt; > > }; > > > > @@ -426,6 +426,7 @@ static inline void z_erofs_exit_zip_subsystem(void) > {} > > #endif /* !CONFIG_EROFS_FS_ZIP */ > > > > #define EFSCORRUPTED EUCLEAN /* Filesystem is corrupted */ > > +#define EFSBADCRC EBADMSG /* Bad crc found */ > > > > #endif /* __EROFS_INTERNAL_H */ > > > > diff --git a/fs/erofs/super.c b/fs/erofs/super.c > > index 0e36949..9cda72d 100644 > > --- a/fs/erofs/super.c > > +++ b/fs/erofs/super.c > > @@ -9,6 +9,7 @@ > > #include <linux/statfs.h> > > #include <linux/parser.h> > > #include <linux/seq_file.h> > > +#include <linux/crc32c.h> > > #include "xattr.h" > > > > #define CREATE_TRACE_POINTS > > @@ -46,6 +47,31 @@ void _erofs_info(struct super_block *sb, const char > *function, > > va_end(args); > > } > > > > +static int erofs_validate_sb_chksum(struct erofs_super_block *dsb, > > + struct super_block *sb) > > +{ > > + u32 disk_chksum, nblocks, crc = 0; > > + void *kaddr; > > + struct page *page; > > + int i; > > + > > + disk_chksum = le32_to_cpu(dsb->checksum); > > + nblocks = le32_to_cpu(dsb->chksum_blocks); > > We cannot write the page data directly since the page cache should be kept > in > sync with ondisk data (or for read-write fs, if it's claimed as uptodated, > and > it is modified later, you should mark it dirty, and do writeback then, but > that is not the erofs case.) > > > + dsb->checksum = 0; > > + for (i = 0; i < nblocks; i++) { > > + page = erofs_get_meta_page(sb, i); > > + if (IS_ERR(page)) > > + return PTR_ERR(page); > > + kaddr = kmap(page); > > Here kmap_atomic(page) is better. what I mean is kmap_atomic() in the > caller > erofs_read_superblock(), it should be replaced to kmap() instead. > > > + crc = crc32c(crc, kaddr, EROFS_BLKSIZ); > > + kunmap(page); > > + unlock_page(page); > > need > put_page(page); > > > I'm not sure whether I explained quite well, but this patch needs something > to do. I'm now working on demonstrating new XZ algorithm and releasing > erofs-utils v1.0. > > You can give more tries or I will help later. :-) > > Thanks, > Gao Xiang > > > > + } > > + if (crc != disk_chksum) > > + return -EFSBADCRC; > > + return 0; > > +} > > + > > static void erofs_inode_init_once(void *ptr) > > { > > struct erofs_inode *vi = ptr; > > @@ -121,6 +147,13 @@ static int erofs_read_superblock(struct super_block > *sb) > > goto out; > > } > > > > + if (dsb->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) { > > + ret = erofs_validate_sb_chksum(dsb, sb); > > + if (ret < 0) { > > + erofs_err(sb, "super block checksum incorrect"); > > + goto out; > > + } > > + } > > blkszbits = dsb->blkszbits; > > /* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */ > > if (blkszbits != LOG_BLOCK_SIZE) { > > -- > > 2.9.3 > > > [-- Attachment #2: Type: text/html, Size: 7119 bytes --] ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH-v2] erofs: code for verifying superblock checksum of an erofs image. 2019-10-22 16:48 ` Pratik Shinde @ 2019-10-22 17:03 ` Gao Xiang via Linux-erofs 0 siblings, 0 replies; 4+ messages in thread From: Gao Xiang via Linux-erofs @ 2019-10-22 17:03 UTC (permalink / raw) To: Pratik Shinde; +Cc: linux-erofs, linux-kernel On Tue, Oct 22, 2019 at 10:18:23PM +0530, Pratik Shinde wrote: > Hi Gao, > > Understood your concern. > > Can we do something like : > > 1) Allocate one buf of size EROFS_BLKSIZ > 2) Read one page at a time into buf(memcpy) .call crc32c for it. > > In this way we won't be writing directly into page data and will not do > large allocation. > What do you think? Yes, that is the right way, but the buf is only be used to calc the 0th block (super_block), for the rest blocks, no need to do this. buf = kmalloc(EROFS_BLKSIZ); memcpy(buf, data); dsb->checksum = 0; crc = crc32c(0, buf); kfree(buf); for (i = 1; i < nblocks; ++i) { page = get_meta_page(sb, i); data = kmap_atomic(page); crc = crc32c(crc, data); kunmap_atomic(data); unlock_page(page); put_page(page); } ... Or some better approach, but it's not ok to modify page cache directly. Thanks, Gao Xiang > > --Pratik > > On Tue, 22 Oct, 2019, 10:04 PM Gao Xiang, <hsiangkao@aol.com> wrote: > > > Hi Pratik, > > > > Some comments as below... > > > > On Tue, Oct 22, 2019 at 09:09:56PM +0530, Pratik Shinde wrote: > > > Patch for kernel side changes of checksum feature.Used kernel's > > > crc32c library for calculating the checksum. > > > > > > Signed-off-by: Pratik Shinde <pratikshinde320@gmail.com> > > > --- > > > fs/erofs/erofs_fs.h | 5 +++-- > > > fs/erofs/internal.h | 3 ++- > > > fs/erofs/super.c | 33 +++++++++++++++++++++++++++++++++ > > > 3 files changed, 38 insertions(+), 3 deletions(-) > > > > > > diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h > > > index b1ee565..4d8097a 100644 > > > --- a/fs/erofs/erofs_fs.h > > > +++ b/fs/erofs/erofs_fs.h > > > @@ -17,6 +17,7 @@ > > > */ > > > #define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING 0x00000001 > > > #define EROFS_ALL_FEATURE_INCOMPAT > > EROFS_FEATURE_INCOMPAT_LZ4_0PADDING > > > +#define EROFS_FEATURE_COMPAT_SB_CHKSUM 0x00000001 > > > > > > /* 128-byte erofs on-disk super block */ > > > struct erofs_super_block { > > > @@ -37,8 +38,8 @@ struct erofs_super_block { > > > __u8 uuid[16]; /* 128-bit uuid for volume */ > > > __u8 volume_name[16]; /* volume name */ > > > __le32 feature_incompat; > > > - > > > - __u8 reserved2[44]; > > > + __le32 chksum_blocks; /* number of blocks used for checksum */ > > > + __u8 reserved2[40]; > > > }; > > > > > > /* > > > diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h > > > index 544a453..cec27ca 100644 > > > --- a/fs/erofs/internal.h > > > +++ b/fs/erofs/internal.h > > > @@ -86,7 +86,7 @@ struct erofs_sb_info { > > > u8 uuid[16]; /* 128-bit uuid for volume */ > > > u8 volume_name[16]; /* volume name */ > > > u32 feature_incompat; > > > - > > > + u32 feature_compat; > > > unsigned int mount_opt; > > > }; > > > > > > @@ -426,6 +426,7 @@ static inline void z_erofs_exit_zip_subsystem(void) > > {} > > > #endif /* !CONFIG_EROFS_FS_ZIP */ > > > > > > #define EFSCORRUPTED EUCLEAN /* Filesystem is corrupted */ > > > +#define EFSBADCRC EBADMSG /* Bad crc found */ > > > > > > #endif /* __EROFS_INTERNAL_H */ > > > > > > diff --git a/fs/erofs/super.c b/fs/erofs/super.c > > > index 0e36949..9cda72d 100644 > > > --- a/fs/erofs/super.c > > > +++ b/fs/erofs/super.c > > > @@ -9,6 +9,7 @@ > > > #include <linux/statfs.h> > > > #include <linux/parser.h> > > > #include <linux/seq_file.h> > > > +#include <linux/crc32c.h> > > > #include "xattr.h" > > > > > > #define CREATE_TRACE_POINTS > > > @@ -46,6 +47,31 @@ void _erofs_info(struct super_block *sb, const char > > *function, > > > va_end(args); > > > } > > > > > > +static int erofs_validate_sb_chksum(struct erofs_super_block *dsb, > > > + struct super_block *sb) > > > +{ > > > + u32 disk_chksum, nblocks, crc = 0; > > > + void *kaddr; > > > + struct page *page; > > > + int i; > > > + > > > + disk_chksum = le32_to_cpu(dsb->checksum); > > > + nblocks = le32_to_cpu(dsb->chksum_blocks); > > > > We cannot write the page data directly since the page cache should be kept > > in > > sync with ondisk data (or for read-write fs, if it's claimed as uptodated, > > and > > it is modified later, you should mark it dirty, and do writeback then, but > > that is not the erofs case.) > > > > > + dsb->checksum = 0; > > > + for (i = 0; i < nblocks; i++) { > > > + page = erofs_get_meta_page(sb, i); > > > + if (IS_ERR(page)) > > > + return PTR_ERR(page); > > > + kaddr = kmap(page); > > > > Here kmap_atomic(page) is better. what I mean is kmap_atomic() in the > > caller > > erofs_read_superblock(), it should be replaced to kmap() instead. > > > > > + crc = crc32c(crc, kaddr, EROFS_BLKSIZ); > > > + kunmap(page); > > > + unlock_page(page); > > > > need > > put_page(page); > > > > > > I'm not sure whether I explained quite well, but this patch needs something > > to do. I'm now working on demonstrating new XZ algorithm and releasing > > erofs-utils v1.0. > > > > You can give more tries or I will help later. :-) > > > > Thanks, > > Gao Xiang > > > > > > > + } > > > + if (crc != disk_chksum) > > > + return -EFSBADCRC; > > > + return 0; > > > +} > > > + > > > static void erofs_inode_init_once(void *ptr) > > > { > > > struct erofs_inode *vi = ptr; > > > @@ -121,6 +147,13 @@ static int erofs_read_superblock(struct super_block > > *sb) > > > goto out; > > > } > > > > > > + if (dsb->feature_compat & EROFS_FEATURE_COMPAT_SB_CHKSUM) { > > > + ret = erofs_validate_sb_chksum(dsb, sb); > > > + if (ret < 0) { > > > + erofs_err(sb, "super block checksum incorrect"); > > > + goto out; > > > + } > > > + } > > > blkszbits = dsb->blkszbits; > > > /* 9(512 bytes) + LOG_SECTORS_PER_BLOCK == LOG_BLOCK_SIZE */ > > > if (blkszbits != LOG_BLOCK_SIZE) { > > > -- > > > 2.9.3 > > > > > ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-10-22 17:04 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-10-22 15:39 [PATCH-v2] erofs: code for verifying superblock checksum of an erofs image Pratik Shinde 2019-10-22 16:34 ` Gao Xiang via Linux-erofs 2019-10-22 16:48 ` Pratik Shinde 2019-10-22 17:03 ` Gao Xiang via Linux-erofs
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).