path: root/doc
authorSergey Poznyakoff <>2016-07-15 11:46:08 (GMT)
committer Sergey Poznyakoff <>2016-07-15 11:57:40 (GMT)
commit44ca2b760b393e993b2a42fc489fa170910ad810 (patch) (side-by-side diff)
tree12aa7390b19bed8aba2535cedb04376c45f820a5 /doc
parent5580c3248794803a8e45dd58b45933a32637954d (diff)
gdbm_open adjusts requested block size to accomodate integer number of directory offsets.
* src/ (GDBM_BSEXACT): New flag. * src/gdbmopen.c (compute_directory_size): New function. (gdbm_open): When creating new database, adjust the requested block size so that the block holds integer number of directory indices. Disable this behavior if GDBM_BSEXACT flag is set (this reverts to old behavior). Always unset GDBM_BSEXACT if using block size returned by stat(2). This makes sure gdbm_open succeeds on file systems reporting block sizes not divisible by 512. * src/gdbmconst.h (GDBM_MIN_BLOCK_SIZE): New constant. * src/gdbmimp.c (gdbm_import_from_file): Use GDBM_MIN_BLOCK_SIZE instead of the hardcoded value. * NEWS: Document GDBM_BSEXACT. * doc/gdbm.texi: Likewise.
Diffstat (limited to 'doc') (more/less context) (show whitespace changes)
1 files changed, 17 insertions, 4 deletions
diff --git a/doc/gdbm.texi b/doc/gdbm.texi
index d172ad7..8096215 100644
--- a/doc/gdbm.texi
+++ b/doc/gdbm.texi
@@ -255,15 +255,20 @@ The arguments are:
The name of the file (the complete name, @code{gdbm} does not append any
characters to this name).
@item block_size
It is used during initialization to determine the size of various
constructs. It is the size of a single transfer from disk to
memory. This parameter is ignored if the file has been previously
-initialized. The minimum size is 512. If the value is less than 512,
-the file system block size is used, otherwise the value of
-@var{block_size} is used.
+initialized. If the value is less than 512, the file system block
+size is used instead. The size is adjusted so that the block can hold
+exact number of directory entries, so that the effective block size
+can be slightly greater than requested. However, if the
+@samp{GDBM_BSEXACT} flag is set and the size needs to be adjusted, the
+function will return with error status, setting the @samp{gdbm_errno}
+variable to @samp{GDBM_BLOCK_SIZE_ERROR}.
@item flags
@kwindex GDBM_READER
@kwindex GDBM_WRITER
@kwindex GDBM_NEWDB
If @code{flags} is set to @samp{GDBM_READER}, the user wants to just read the
@@ -284,12 +289,18 @@ The following may also be logically or'd into the database flags:
@samp{GDBM_SYNC}, which causes all database operations to be
synchronized to the disk, @samp{GDBM_NOLOCK}, which prevents the library
from performing any locking on the database file, and @samp{GDBM_NOMMAP},
which disables the memory mapping mechanism. The option @samp{GDBM_FAST} is
now obsolete, since @code{gdbm} defaults to no-sync mode.
+@kwindex GDBM_BSEXACT
+If this flag is set and the requested @var{block_size} cannot be used
+without adjustment, @code{gdbm_open} will refuse to create the
+databases. In this case it will set the @samp{gdbm_errno}
+variable to @samp{GDBM_BLOCK_SIZE_ERROR} and return @samp{NULL}.
@cindex close-on-exec
If the host @samp{open} call
(@uref{, open(2)})
@end ifhtml
@@ -1230,15 +1241,17 @@ No error occurred.
Memory allocation failed. Not enough memory.
+@kwindex GDBM_BSEXACT
This error is set by the @code{gdbm_open} function (@pxref{Open}), if
-the value of its @var{block_size} argument is incorrect.
+the value of its @var{block_size} argument is incorrect and the
+@samp{GDBM_BSEXACT} flag is set.
The library was not able to open a disk file. This can be set by
@code{gdbm_open} (@pxref{Open}), @code{gdbm_export} and
@code{gdbm_import} functions (@pxref{Flat files}).

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