linux-ext4 - Re: [PATCH v3 00/15] Fast commit changes for e2fsprogs

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Date:   Thu, 21 Jan 2021 00:22:25 -0500
From:   "Theodore Ts'o" <tytso@....edu>
To:     Harshad Shirwadkar <harshadshirwadkar@...il.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH v3 00/15] Fast commit changes for e2fsprogs

On Wed, Jan 20, 2021 at 01:26:26PM -0800, Harshad Shirwadkar wrote:
> 
> - Fix compilation error by defining jbd2_journal_get_fc_num_blks (also
>   rename it to jbd_get_fc_num_blks) as a preprocessor macro instead of
>   inline function which gets compiled out when "-g" is passed

Unfortunately, this still doesn't quite fix things.  The problem with
this approach is the preprocessor macro uses be32_to_cpu(), which gets
turned into ext2fs_swab32().  And the libe2p shared library is not
allowed to depend on libext2fs.  Otherwise when we build with
configure --enable-elf-shlibs, the link of misc/chattr fails with:

<tytso@...c> {/build/e2fsprogs/misc}  
1078% make V=1
../util/subst -f ../util/subst.conf /usr/projects/e2fsprogs/e2fsprogs/lib/dirpaths.h.in ../lib/dirpaths.h
gcc   -Wl,-rpath-link,../lib -o chattr chattr.o ../lib/libe2p.so ../lib/libcom_err.so  \
	 
/bin/ld: ../lib/libe2p.so: undefined reference to `ext2fs_swab32'
collect2: error: ld returned 1 exit status
make: *** [Makefile:636: chattr] Error 1

We had already defined e2p_be32() and use it in other places in
lib/e2p/ljs.c.

So I fixed this by taking your Dec 10th version of the patch series,
and making the following change to patch 4/15:

diff --git a/lib/e2p/ljs.c b/lib/e2p/ljs.c
index 9f866c7e..59728198 100644
--- a/lib/e2p/ljs.c
+++ b/lib/e2p/ljs.c
@@ -36,6 +36,17 @@ static __u32 e2p_swab32(__u32 val)
 #define e2p_be32(x) e2p_swab32(x)
 #endif
 
+/*
+ * This function is copied from kernel-jbd.h's function
+ * jbd2_journal_get_num_fc_blks() to avoid inter-library dependencies.
+ */
+static inline int get_num_fc_blks(journal_superblock_t *jsb)
+{
+	int num_fc_blocks = e2p_be32(jsb->s_num_fc_blks);
+
+	return num_fc_blocks ? num_fc_blocks : JBD2_DEFAULT_FAST_COMMIT_BLOCKS;
+}
+
 static const char *journal_checksum_type_str(__u8 type)
 {
 	switch (type) {
@@ -58,7 +69,7 @@ void e2p_list_journal_super(FILE *f, char *journal_sb_buf,
 	int journal_blks = 0;
 
 	if (flags & E2P_LIST_JOURNAL_FLAG_FC)
-		num_fc_blks = jbd2_journal_get_num_fc_blks((journal_superblock_t *)journal_sb_buf);
+		num_fc_blks = get_num_fc_blks((journal_superblock_t *)journal_sb_buf);
 	journal_blks = ntohl(jsb->s_maxlen) - num_fc_blks;
 	fprintf(f, "%s", "Journal features:        ");
 	for (i=0, mask_ptr=&jsb->s_feature_compat; i <3; i++,mask_ptr++) {