git: 077f757d72e5 - main - newfs_msdos: align data area to VM page boundary by default

The branch main has been updated by se:

URL: https://cgit.FreeBSD.org/src/commit/?id=077f757d72e561eb84193d8e58f63e96e69b8096

commit 077f757d72e561eb84193d8e58f63e96e69b8096
Author:     Stefan Eßer <se@FreeBSD.org>
AuthorDate: 2024-06-02 12:07:52 +0000
Commit:     Stefan Eßer <se@FreeBSD.org>
CommitDate: 2024-06-02 12:07:52 +0000

    newfs_msdos: align data area to VM page boundary by default
    
    Without alignment, the data area will not be aligned with the buffer
    cache, leading to overhead, higher write multiplication on SSD devices
    and issues with very large cluster sizes (see PR 277414).
    
    The -A option used to align the start of the root directory to a
    multiple of the cluster size, which happens to align the start of the
    data area with a buffer page boundary in case of large clusters and
    the default number of directory entries (512 entries requiring 16 KB
    for FAT12 or FAT16, FAT32 puts the root directory into the data area).
    
    This commit aligns the start of the data area with the page size, if
    neither -A nor -r is used. It changes -A to align the start of the
    data area (end of the root directory) to a multiple of the cluster
    size, since this is the alignment that prevents write multiplication
    due to clusters crossing erase block boundaries of a SSD device.
    The -r option is unchanged and will prevent any automatic alignment
    from occuring.
    
    Approved by:    kib
    MFC after:      1 week
    Differential Revision:  https://reviews.freebsd.org/D45436
---
 sbin/newfs_msdos/mkfs_msdos.c  | 26 ++++++++++++++++++--------
 sbin/newfs_msdos/newfs_msdos.8 | 16 ++++++++++++++--
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/sbin/newfs_msdos/mkfs_msdos.c b/sbin/newfs_msdos/mkfs_msdos.c
index 065e3c5f4192..423fbbcadcc5 100644
--- a/sbin/newfs_msdos/mkfs_msdos.c
+++ b/sbin/newfs_msdos/mkfs_msdos.c
@@ -249,7 +249,7 @@ mkfs_msdos(const char *fname, const char *dtype, const struct msdos_options *op)
     ssize_t n;
     time_t now;
     u_int fat, bss, rds, cls, dir, lsn, x, x1, x2;
-    u_int extra_res, alignment, saved_x, attempts=0;
+    u_int extra_res, alignment, alignto, saved_x, attempts=0;
     bool set_res, set_spf, set_spc;
     int fd, fd1, rv;
     struct msdos_options o = *op;
@@ -412,8 +412,12 @@ mkfs_msdos(const char *fname, const char *dtype, const struct msdos_options *op)
 	}
 	bpb.bpbFATs = o.num_FAT;
     }
-    if (o.directory_entries)
-	bpb.bpbRootDirEnts = o.directory_entries;
+    if (o.directory_entries) {
+	bpb.bpbRootDirEnts = roundup(o.directory_entries,
+	    bpb.bpbBytesPerSec / sizeof(struct de));
+	if (bpb.bpbBytesPerSec == 0 || o.directory_entries >= MAXU16)
+	    bpb.bpbRootDirEnts = MAXU16;
+    }
     if (o.media_descriptor_set) {
 	if (o.media_descriptor < 0xf0) {
 	    warnx("illegal media descriptor (%#x)", o.media_descriptor);
@@ -564,14 +568,20 @@ mkfs_msdos(const char *fname, const char *dtype, const struct msdos_options *op)
 	    x1 += (bpb.bpbBigFATsecs - 1) * bpb.bpbFATs;
 	}
 	if (set_res) {
-	    /* attempt to align root directory */
-	    alignment = (bpb.bpbResSectors + bpb.bpbBigFATsecs * bpb.bpbFATs) %
-		bpb.bpbSecPerClust;
 	    if (o.align)
-		extra_res += bpb.bpbSecPerClust - alignment;
+		alignto = bpb.bpbSecPerClust;
+	    else
+		alignto = PAGE_SIZE / bpb.bpbBytesPerSec;
+	    if (alignto > 1) {
+		/* align data clusters */
+		alignment = (bpb.bpbResSectors + bpb.bpbBigFATsecs * bpb.bpbFATs + rds) %
+		    alignto;
+		if (alignment != 0)
+		    extra_res += alignto - alignment;
+	    }
 	}
 	attempts++;
-    } while (o.align && alignment != 0 && attempts < 2);
+    } while (alignment != 0 && attempts < 2);
     if (o.align && alignment != 0)
 	warnx("warning: Alignment failed.");
 
diff --git a/sbin/newfs_msdos/newfs_msdos.8 b/sbin/newfs_msdos/newfs_msdos.8
index efa69c058453..816b5fc867b4 100644
--- a/sbin/newfs_msdos/newfs_msdos.8
+++ b/sbin/newfs_msdos/newfs_msdos.8
@@ -23,7 +23,7 @@
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 .\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd January 12, 2024
+.Dd June 2, 2024
 .Dt NEWFS_MSDOS 8
 .Os
 .Sh NAME
@@ -91,7 +91,13 @@ A suffix s, k, m, g (lower or upper case)
 appended to the offset specifies that the
 number is in sectors, kilobytes, megabytes or gigabytes, respectively.
 .It Fl A
-Attempt to cluster align root directory, useful for SD card.
+Attempt to cluster align the data area, useful for SD card.
+If neither the
+.Fl A
+nor
+.Fl r
+option is used, the number of reserved sectors is set to a value that aligns
+the start of the data area to a multiple of the page size of the host.
 .It Fl B Ar boot
 Get bootstrap from file.
 .It Fl C Ar create-size
@@ -167,6 +173,12 @@ is 2.
 Number of hidden sectors.
 .It Fl r Ar reserved
 Number of reserved sectors.
+If neither the
+.Fl A
+nor
+.Fl r
+option is used, the number of reserved sectors is set to a value that aligns
+the start of the data area to a multiple of the page size of the host.
 .It Fl s Ar total
 File system size.
 .It Fl u Ar track-size